The news about BuddyPress has fully shifted my attention from single-blog WordPress installs to multi-user, multi-blog installs.
WordPress mu is my platform of choice, but I was quite fond of Lyceum when I first learned of it a while ago. The big perceived advantage of Lyceum is that it uses a unified table structure for all blogs, rather than creating a new set of tables for each blog as WPmu does. I’m not so sure that’s important now, and WPmu’s scheme now looks a lot easier to partition onto multiple database servers, should traffic ever scale there. Still Lyceum is an interesting project, and their name and logo are great.