How stable is it on PS3? I've heard their Ultimate Edition is about as unplayable as the base game was when it launched.
Oi no, that's the exception.
As we've discussed in previous threads, the PS3 issues actually originated in New Vegas, hence why Bethesda must've known about it when producing Skyrim: because they watched Obsidian struggle to fix it, with the end statement of New Vegas' project director being "PS3's design and the Bethesda game engine just DO NOT mix," basically.
It IS playable on PS3 and stable when it does work, but you have to be willing to accept that by the time you've completed, say...many of the main game sidequests and two of the DLCs, it's time to start a new character. Basically the character file size, as it grows, slows down the game, and something about visiting the DLCs slows it down quite a bit, so managing to visit all four on one character isn't so likely.
If you can avoid buying it for PS3, even if it means buying it for PC and playing on minimum graphics settings, do it. Some people report having flawless copys of the Ultimate Edition, but it's 50-50, which is still pretty bad odds.
Take a look at the New Vegas PS3 forum, for an idea. Or hell post your own thread and ask people if they have issues with it or not.
But New Vegas is definitely worth getting if you can. It's ridiculously better written than anything Bethesda's ever produced, characters have realistic, believable personalities with multiple layers, weapons and armor are balanced, there's multitudes of ways to build various powerful characters, etc etc etc.