My gaming club has no board per se, but rather drags a few tables together, throws a dropcloth over them, and places terrain pieces on top. Works quite nicely. On the home front, my house is too small for a full blown table, but i have been helping a small group of friends to build a table in a friend's basement, themed around mars. (Red soil, short hills, outposts dotting the table, things like that.)
I prefer large tables rather than small, as my grey knights tend to die less when there's space between me and the enemy, and i love to see the look on my opponents face when my entire SM army infiltrates across 2/3 of the table and totally blows his plans to high hell. But that's more of a personal thing, as my armies are tuned towards large tables.