I think Karsten Rutledge covered almost everything, but I've got one more.
The thing that totally sold me on SL is the scripting, and it's REALLY frustrating when I run into things that can't be scripted. I'll buy some of the reasons, like not spamming the asset server with scripts writing to notecards, but there's too much stuff you simply can't do from scripts, that do not require a complicated new paradigm to allow from scripts, and that if I had source code access would be implemented by now.
llReturnObject(key id);
llTeleportAgent(string region, vector offset);
llTeleportAgentInRegion(vector offset);
key llRequestAgentGroups(key id);
key llRequestNextAgentGroup(key dataserver_id);
llSetLinkParams(integer link, list params);
llSetLinkListParams(list links, list params);
string llGetInventoryDescription(string name);
key llGetInventoryOwner(string name);
llSetAnimationOffset(vector offset, rotation rotation);
key llGetClothes(integer clothes_id); // CLOTHES_UNDERSHIRT ... CLOTHES_SOCKS
llWearClothes(integer clothes_id, key id);
instant_message(key sender, string name, string message) {...}
key llRequestTransactionInfo();
key llRequestNextTransaction(key dataserver_id);
Plus things like the rotation parameters for avatars, control keybindings for things like "fly" or "stop flying" and function keys...
This is stuff that shouldn't need a feature vote, "add API for everything there's a UI for" and "make sure there's an API for every new feature" should be at the top of the BLOTTD because it's so damn *easy*. What am I missing?