...I was going to Best Buy for some DVD+Rs, when off by the computer section they had an XBox 360 playing Guitar Hero 2 on display (and a second Wii display)...and to my amazement there was another XBox 360 playing a demo of RockBand, complete with the Stratocaster, microphone, and drums. I only played the drums for about a minute (on hard), I don't really know if I was doing bad or good. I switched to guitar and played 'Say it Ain't So' on Expert, and whooped it's ass - after playing miserably for a minute in the beginning. The guitar, while basically having the same layout as the Guitar Hero guitars, takes some getting used to. The buttons are much bigger, and there's no gap between them, so it's kind of hard to tell where your fingers are laid out. I hope this is a very early beta or something, because the guitar part for 'Say it Ain't So' actually follows the bass line, which doesn't make any sense - maybe on easy it should, but the guitar (during the verses) is completely different than the bass, although based on the same rhythm. The drum solos you can do are pretty awesome, and are pretty realistic. I wish there was a bass drum pedal though, instead of the game hitting the bass drum for you. From my (very short) experience - the drums are awesome, but as far as guitar parts are concerned, Guitar Hero 3 (and GH2...and GH1) are better, and by quite a bit.
Edit - once again my hook-up has come through, and I've got Rock Band, the game, not the full kit. I'm not going to buy the guitar, because the one at Best Buy broke (you can only do up-strokes), which makes me believe it sucks, and also I have 2 GH2 X-Plorers already (I'm going to trade in one of them for a Les Paul when I can find one). I've already breezed through the first set on Expert, but the second set looked boring, so I gave it a break for now. I'm now jsut looking forward to Tuesday so I can (hopefully, since I'm working all day) find a drum set, as that's what I'm really looking forward to in this game (and playing the sh!t out of Enter Sandman).