From: Tod69 Talamasca
As with ANY program, the key to Efficiency is learning the Shortcut Keys.

I would take issue with shortcuts being "THE key" to efficiency. They can be highly useful, sure. But it's entirely possible to be extremely efficient without ever using them.
I would say "the key" is in discovering the underlying logic behind the program, in getting inside its authors' heads as best you can, so you'll have a reasonable idea of what to expect at every turn. Lots of people call me "Photoshop guru", as if I know everything there is to know about the program. But the truth is I actually "know" very little about it. I do intuit quite a lot about it, though, all the time. My level of expertise comes maybe 5% from knowledge, and 95% insight, always.
I haven't invested much, if any, time into memorizing Photoshop's countless thousands of procedures. I've simply attuned my view of it, and my approach to it, in such a manner that I can intuit the procedure for any given task with relative ease. Ask me how to do something with it, and I'm not gonna flip through some mental encyclopedia of procedures to find the right one. I'll simply think and feel my way through the process to make my way to the desired outcome.
I'm nowhere near good enough at memorization to "know" all that much about anything. I'm just smart enough to realize that "knowing" isn't as important as understanding, at least for me. In other words, as I see it, learning the "why" behind something usually eliminates the need to learn the "how". And since there are generally a lot less why's than how's in the world, going with the why's is a lot easier, a lot more "efficient".
So for me, shortcuts aren't much of a "key" to anything, except a few less mouse clicks here and there for the ones I happen to know. And the only reason I know as many of them for Photoshop as I do is that during the final few months of my old computer's useful lifespan, before I got my current one, PS and SL had been fighting with each other a lot. Whenever SL was running, if I would try to pull down a menu in PS, the computer would freeze for a minute. This was just annoying enough to prompt me to use as many shortcuts as I could, to avoid menus wherever possible. Before that, though, I used PS for years without using ANY shortcuts at all. And I think it's safe to say I was pretty darned efficient with it the whole time.
"Efficiency" to me means the ability to achieve a successful outcome with consistent high confidence and speedy deliberation, based on understanding. It's not about memorization of steps (including memorizing shortcuts), or about using the lowest possible amount of mouse clicks.
I guess we look at it differently.
From: Tod69 Talamasca
Although I gotta admit some of these shortcut keys seem odd compared to Photoshop, but I think that's part of an IP thing (can't use the same ones as PS for the same function without running afoul of Adobe's Lawyers). Even interfaces fall under the whole copyright thing.

I can't pretend to know the real motivations behind what shortcuts anyone creates, let alone the authors of GIMP, but I would tend to doubt it's got anything to do with IP, Tod. Lots of shortcuts are the same in all kinds of programs. Ctrl-Z, for example is almost universal for undo. Ctrl-N is almost always a safe bet for New File. Ctrl-S is usually Save. Etc., etc., etc.
Photoshop and PSP actually have a number of shortcuts in common. B for the paintbrush, for example, V for the move tool, E for the eraser, etc. There are, of course, a ton that are different as well, but a good portion are the same.
Even if a set of shortcuts were to be considered protected as IP, though, which would really surprise me if it were to happen, it wouldn't have anything to do with copyright. A keyboard shortcut is a function, not a work of literature or art, so copyright can't apply. Copyright has nothing to do with function or functionality.
To illustrate the difference, let's take a step away from the computer for a second, and take a look at another well known example of where copyright can't apply, clothing design. Knock-offs of designer clothing are legal because the design of a garment is considered to be functional, not artistic, no matter how elaborate or original looking the garment might be. The pattern printed on a piece of cloth could be copyrighted, but the manner in which you choose to cut, fold, stitch, and hem that cloth to turn it into an article of clothing is purely functional, under the legal definition. Anyone else could take any piece of cloth, cut, fold, sew, and hem it the same way, and produce a similar looking garment, without violating copyright. The only thing they couldn't do would be to reproduce pattern of the cloth itself without permission.
That same logic applies to in-program tools. The icon that appears on-screen for a tool could certainly be copyrighted, as could any written instructions for its use. Just like the aforementioned cloth pattern, the icon is a work of art, and the instructions are a work of literature. Copyright applies to both. However, the mapping of a key to the selection of a tool is a function. Copyright cannot apply to that.
If any IP protection vehicle were to be applicable, it would be a patent. Patents protect processes, and it's arguable that the pressing of a button to trigger the selection of a tool is a process.
However, it would be extremely unlikely anyone would ever be granted a patent for a keyboard shortcut, since it would be pretty much impossible to argue that one is an original idea. Just because I might want to assign the key labeled A to a given tool in my program, and you might choose the one labeled B for the same kind of tool in your program, doesn't reasonably qualify your use of B as a new invention. Even if no one else ever happened to have mapped that particular key for that specific tool ever before, it doesn't change the fact that all you did was use a keystroke to trigger tool selection, which is a common practice. The specific key involved is irrelevant.
OK, back to copyright. What parts of an interface can be copyrighted, you might ask. The answer is icon images (already mentioned) and other pictures, any original music or sounds, any on-screen animations or other kinds of video, and anything with a fair amount of original text in it. The wording of a Help file, for example, could certainly be copyrighted, as could the look of a splash screen.
So what bout the names of tools and menu items? Names of things cannot be copyrighted, ever. That's not what copyright is for. Names fall under trademark. Not just any name of any item can be trademarked, though. It has to be uniquely identifiable with its maker in order for trademark to apply. In most cases, tool names don't fit that description. Every paint program on Earth has a tool called "paintbrush", for example. It would be pretty tough for someone to argue that their own particular use of it is so uniquely tied in with their particular identity as to warrant a trademark. Once something has been so genericized, trademark exclusivity is no longer applicable.
It would be like if you created a RL tool brand called Screwdriver, and then trying to say that no one else can use that word from now on to describe a tool for turning screws if it wasn't made by you. That wouldn't hold up. The word "scredriver" has been in use for that purpose for centuries. You can't just come along and change its meaning.
To summarize all this, copyright has relatively little to do with interface design. Patents and trademarks similarly have little to do with it by themselves. Put the three together, though, and you might have something. Your code can be copyrighted, as can your icons. The (unique) manner in which your particular program works can be patented. And its name can be trademarked. All in all, this means your program is legally YOURS, and cannot be duplicated without your consent.
That doesn't mean, however, that no part of it can be imitated. Something as mundane and commonplace as a keyboard shortcut always can be reused.