I concur with a large galactic map with slow travel times (which supports a single server cluster, not multiples... and to think about, no worries about a server merge). By having either a large galactic map or slow warp travel times or both, this keeps players to confined to given sectors. This also allows players to developer specialized knowledge of the areas that they are at (ie: Romulan/Federation Sector) and provides more fun experience when moving out to other sectors. Each sector is essentially its own server cluster (Romulan/Federation Server, Klingon/Romulan Server, Federation Deep Space Server, etc), but unlike other games, each server is connected to one another by the proxy server (Galactic Server).
Depending on the technology of the platform, a seamless transition between sectors may not be possible (may have loading screens), but I think that would be a worthwhile trade-off when leaving one sector and entering another.
There is one problem though that I see when using either large maps and/or slow movement, and that is player density. For example, the happening place is the Federation/Klingon Sector, whereas the Klingon Deep Space Sector is pretty much dead (Who wants to be a Klingon Explorer?). So a Klingon player who is out exploring gets bored since there appears to be nothing to do out here, no one to talk to... all the cool kids are at the border. The player wants to join this popular guild, but it is way across Klingon Space.
Since the player can get into the guild instantly, the fear is, the player will quit. This then leads to where every Player is Special and needs instant gratification.... Whereas the strong gamers (everyone is not special, to become special means to earn it), they realize that is how being in a big galaxy on the fringe of civilization works.
