Heh, don't take this the wrong way, but compairing what you can do in SL to any of the "crafting" systems I've seen is like compairing pong to the PS2. It's closer to making a HalfLife mod, but even blows that away in many aspects - it's just that you can do soooo much more in SL as far as customizing/making anything you can envision. But, since I like the analogy anyways, let me break it down like this for you.
The "Guilds" of SL 
-
BUILDER/Architect/Weaponsmith - (Some geometrical and artistic skills add a bonus of + 1, 3D rendering experience +2)
Right click and "create" a prim, you can make them in a number of shapes, and then link a group of them together to create "objects" An object can be anything from a car to a house to, well, anything you can represent in 3-D space out of these building blocks.
TEXTURER/Artist/Clothes Maker - (Somewhat artistic +1, Experience with Photoshop +2)
Using an external program like Photoshop, Paint Shop, or any other image editor, you can make/draw the textures that are painted onto the objects that builders make. OR, you can also use the clothing templates and design the textures that become the clothes people wear.
ANIMATOR/Dance Instructor/Sex Therapist - (Experience with Poser +2)
You can create poses and animations for your AV or to sell to other AV's using poser.
SCRIPTER/Programmer/Engineer - (Good with math and logic +1, Any computer programming experience +2)
Finally, you can learn "LSL", the Linden Scripting Language, a built in programming language that lets you make vehicles run, doors open/shut/lock, and do many, many, many more things.

I guess most people who are "financially successful" through SL either utilize some or all of the "skills" or "guilds" listed above, or are part of a larger network/"party"/business that creates and sells content... For example, lets say you start looking at SL and find that you can build and script. Maybe you build a boat and can put a script in it to make it run, but the sails and everything else it's composed of are made of wood - You can either find someone who can make a good sailboat sail texture, or learn to use a graphics editing program yourself and make your own sailboat sail. Then, once you have your completed boat, you can sell copies of that boat to other people in SL, and then use the money to go buy things you like in SL.
One of the best things about SL is that it's hard to define and "put in a box" - Lets say you're a musician and you're good with that and nothing else. Well, you can DJ or perform live concerts in SL, or hire a scripter to put different audio samples you make into a keyboard or DJ-table, ect, ect... The limit isn't some defined craft recipe or level cap - If you put the time, effort, and creativity into it, you are limited almost only by your imagination.