Friends lists and in-game chat is nice, but what I'd really like to see is server tags. I realize I've requested this before, but it's worth repeating.
The default server browser is functional but mediocre; it would be significantly better if servers could be filtered by content. The simplest implementation I can think of is that you, Ephialtes, manually generate the list of tags and server owners select up to three that best describe their server.
Examples:
Theme tags: Space, Western, Underwater, City, Medieval
Game-play tags: RP, DM, Mining, Freebuild, Themebuild
A slightly more difficult feature would be a server quality index. I'll leave the exact calculation up to you, but you could consider factors like: the # of players that connect, how long they stay, if players return and if so how often, server up-time, amount of custom content enabled, etc. Such an index might provide an incentive for players to host good servers and thus improve the game's value for its players.