from what i understand, rock band has a full single-player mode, and i\'m pretty sure you can do single-player with any instrument too. plus, get a mic stand and you can do vocals and either guitar/bass/drums at the same time.
the 360 recently had a price drop, albeit a small one. i do have a Wii, but don\'t particularly consider it \'next gen\'. i\'d feel more comfortable waiting a bit longer to get a next gen system (read: until microsoft makes a 360 that isn\'t a time bomb or sony gets some decent games and an online environment half as good as xbox live), but rock band is sort of forcing me to make the move now. i\'ll be picking up a 360 and guitar hero 3 on october 27th (though that\'s probably the 23rd, as saturday is a weird release day).