A Random Battle from last week fought over why MMOs use servers to keep you from playing with your friends. I have had a couple dozen friends play City of Heroes over time, but being spread across servers was always an issue that kept us from meeting up, joining together, and keeping them from quitting. There have been previous notes that chat and auction houses go across servers in City of Heroes.
When testing server transfers, Cryptic mentioned that they are looking at a potentially server-less game, in which you can team with anyone regardless of server. I imagine this could be done either as putting everyone on one big server or allowing teams to enter instanced missions from the doors on their respective servers. The follow-up clarified that this is a “maybe, someday” idea, not a “next issue, we promise!” idea. If they do it, not in 2007.
That would be really cool. It feels a little like slipping toward Guild Wars or Diablo as a model (big joint chat room leads to instances), but if you can never have an impact on the game world anyway, why not share that game world instead of making little copies of it? Of course, if you all shared one world, you could let players influence it without worrying about maintaining story and development across divergent shards…