[_ck_]

Memcache is going to be an absolutely useless suggestion for 95%+ of bbPress users.

Most won’t have the knowledge or resources to set it up and the performance boost will be trivial, almost non-existent for a single server setup (on a shared host it won’t even be a possibility). A proper mysql cache, opcode cache, and local disk cache will come within the same single digit performance gains of memcache.

Memcache is only beneficial for multi-server systems, it’s why it was invented in the first place.

The way to cache forums properly is to cache parts of the pages and build the page based on each user on demand. This allows much more dynamic content.

Large forums usually have an additional problem with several bots crawling them at once at any given time which is why caching every single page in a page cache (like wp super cache) can be a problem. The bots will fill the cache with many one-time hits which have to be purged very soon after they are created.