I have a 12" iBook G4/1.42GHz and an iPad 1 would be a welcome upgrade. Don't bother with the iBook, it doesnt' do YouTube very well (very choppy) and otherwise only the most basic web browsing works for it.
You can always use MacTubes to watch YT videos without much, if any, real performance drop - it's really a boon because it allows you to avoid Flash, even on Intel machines.
Back to the actual question... For $250, I'd say no, and if you really want a netbook you could try to stick OS X onto a compatible netbook in that price range. It might perform better - at least, CPU-wise. (The GMA950 is nasty, though.) That, or, as others have mentioned, an iPad.
If you can find a cheaper iBook, though, it might be worth it. Just make sure it's a 2005 model - the Radeon 9550 in these will be a big boon to performance, whether you're running Tiger or Leopard.