Cool Spotify trick
Ever wonder how deep the Spotify catalog is? Spotify won't tell you directly, but you can figure it out pretty easily. Spotify lets you search their catalog by date - so a search like this: spotify:search:year:0-3000 will return the entire catalog, which lets you view their stats:
Total tracks: 3,586,179
Total albums: 319,106
Total artists: 264,461
Spotify orders their results (apparently), by popularity, so the search results for this 'all music' query not only shows you the size of the Spotify catalog, it shows you what are the most popular tracks in the entire catalog, which happens to be topped by Lady Gaga, The Killers, Beyoncé, and Coldplay. This popularity sort is pretty handy when combined with the year-based seach. You can quickly and easy listen to the most popular songs of any year - here's the year I graduated from high school: 1977 at Spotify.
With 40K new users signing up every day, Spotify is capturing the music world. It will be really amazing to see what happens if/when they open their doors in the U.S.