Re: BP could handle a huge number of members?
WordPress scales just fine. Is it perfectly and sveltely built for all applications? No.
http://ma.tt/2006/03/wordpress-and-lyceum/ is a good read about this from a few years back. 
BuddyPress doesn’t really suffer any of these as advantages or disadvantages, since it currently sits on top of an MU installation; it just kinda “is.”
