Space Empires Debot was the first SE centre and started the RP and storytelling movement.
Currently no such centre exists. SpaceEmpires.org while maintained by Hadrian was such a place but now the place is in the future.
Here's a promising website. While not a centre it is a gathering place for a different part of the community and might well become more a general centre in the near future:
http://www.solar-outpost.com
BTW narf, most of those people are there
