A client of mine who is on a Dreamhost shared hosting account wants to give Buddypress a test drive. I was chagrined to learn that Dreamhost no longer allows WordPress MU to be installed on any shared hosting account (WordPress MU is the engine that runs Buddypress). Dreamhost used to allow it to be installed, and some time in the last year or so stopped doing so. Dreamhost claims that WordPress MU is too resource-intensive to be economical for them on a shared hosting account. This sucks (even if it does make sense).
Lucky for us, HostGator allows WordPress MU on their shared hosting accounts!