On Tuesday, October 26, we will begin removing friends from users who exceed our limits on the number of friends you can have, depending on whether you are VIP or not. VIPs can have up to 500 friends, and non-VIP users have to settle for 100. We've created a machine that can remove friends from those who have too many. It will check when the friends were last online, if they were recently written to (both in direct messages and on the profile), and see if you have added the friend as a favorite. If a friend is marked as a Favorite, this friend probably won't be removed from your friends list.
As a bonus, you now get a small notification when one of your favorite friends comes online. Another small reason why it is more fun to be a VIP member.