Re: WP-Super-Cache Question
WPSC has a “don’t cache for logged in users” setting, which you might want to use given the nature of a BP site.
I’ve seen various people also recommending WP Object Caching, which can reduce the load on the DB server and might be worth looking into *if* your performance bottleneck is the DB… if it isn’t, then it could make matters worse. Use the page generation time and (to a lesser extent) the number of queries information that the default templates show in an HTML comment at the bottom of most templates to test your options both with and without whatever caching you put in.
Useful links: Overview of WP Object Cache from 2006 for an intro, various flavours of Object Cache (APC, eAccelerator, filesystem) (if you dig around you’ll also find one which works with memcached).