I play about 14-20 hours of Rock Band a week depending. I can't remember the last time I didn't play RB on any given day, usually about an hour or two of solo play or up to 3-4 (sometimes 5-6) hours of online play with friends. I've played a lot of different songs; I have 400+ DLC, only because I had to delete some to make room in my 60GB hard drive, though I'll be switching to a 120GB in the next week or so. Up until my HD space got inescapably cluttered I would frequently purchase and download the newest DLC (though not quite to the extent of buying every last song).
I love playing new songs as long as they're fun, regardless of my musical taste for them. I've been playing rhythm games for about 5 years now starting with GH2, and I bought RB1, RB2 and TB:RB on release day. I play every instrument pretty dang well on expert, mostly drums and vocals lately though I also have tons of experience on bass. I think I'm a pretty good judge of a chart's quality, and have a keen ear for what's going on in the background of a song. I'm really excited for what this service offers, and hope I'm lucky enough to get in on it!