I think everyone either runs their own corp (like I do so that it's easier to share inventory amongst characters) or has joined a big corp to play with.

I tried to form an alliance of multiboxer corps with Souca a while back but it turns out that alliances are expensive in terms of extra skills and running costs. Still like everything in EVE you learn by trying.

But I'd be up for creating and/or joining a multiboxing corp if anyone is interested? Although there's always the problem of everyone having their own favourite patch of space to play in.