The visibility of other people who you want to hang out with in a game is of the utmost importance -- even more so is the ability to converse with them. Why even bother playing an MMO for more than a few weeks if you can't grasp the feeling of being around, and interacting with, at least several people on a consistent basis?
It always strikes me as surprising when any new game doesn't feature a robust, flexible and slick chat window. Something as simple as a great chat window can play a very large role in the success of an MMO, because it's the primary means of communication between all players. A chat window needs to epitomize a responsive, useful and meaningful tool of exchanging information. This seems like an obvious thing to say, but so many games get it wrong that it amazes me. Warhammer Online is the perfect example of a chat window that needs a lot of attention. So much of that game is done right, but this is one of its biggest failings and while it's not debilitating it does hurt the game's community.
Even with a good chat interface, there's much more that could be done. Besides, everyone knows a chat window is only as good as the people chatting within it. Community needs to become more prominent, it needs to become more visible earlier on. MMO developers need to take a harder, longer look at social networks. They're immensely popular for a reason: people love to find other people with the same interests as them. Create a system within a game that's somewhere between a guild and a Facebook group and I guarantee something special will happen.
Of course some developers are already working on websites that are essentially Facebook for their games. That's a great start, but the smart choice would be to integrate Web 2.0 concepts directly into a game's infrastructure from the ground up. And why not? It's not as though it couldn't be done and people are absolutely waiting for a great (or even simply good) game that does the social thing extremely well. MySpace is a testament to how much people will put up with sloppy design and code for a strong sense of community, if I ever saw one. The sooner someone figures it out, the bigger their splash is going to become.