Right now my collection stands at 51.6 GB, encompassing 6,243 tracks that would take me 506 hours (or 21.08 days) to play through before it started repeating. As for my media player of choice, I find Windows Media player 11 to suffice for just about everything, though I will utilize Media Player Classic every so often.
I still have a ton of music I need to rip to my computer (and several CDs I need to track down, followed shortly by meting out some well deserved beatings for taking them), and I compulsively buy new music, so I expect that number will continue to steadily rise (less than a year ago it was under 8 gigs).