EDIT: Just cancelled my order. I was lurking around the official Rock Band 3 forums and was shocked to see a massive topic concerning freezing / crashing issues of the PS3 version. Apparently there was a patch released in April that royally screwed the game up and has yet to be fixed. It seems to crash to the XMB if you are signed in to PSN, whether you're playing online or locally. It doesn't appear to occur if you simply stay completely offline and not log into PSN at all. But that basically destroys at least 50% of the game right there.
I picked up RB3 for around $15 as well a few months ago, and I realize this is anecdotal, but I haven't experienced anything like that, and I've put some solid hours into the game. I understand your hesitation, though.