The average Spotify listener listens to 50 new tracks a month

"The changes we’re having to make will mainly affect heavier Spotify Free and Open users, as most of you use Spotify to discover music – on average over 50 new tracks per month, even after a year. Plus, the average user won’t reach the limit on plays for 7 out of 10 tracks, after a year of using Spotify. For those of you using Spotify to find new tracks to enjoy and share with friends, these changes shouldn’t get in the way of you doing that. Rest assured that we’ll continue to bring you the biggest and most diverse music catalogue available."
Source:  Blog post from Spotify (announcing restrictions to the free service), 14th April 2011
Note - By 'new' what they mean is tracks that user had not listened to before