Re: upgrading from trac
@Matt. WPMU 2.9 not BP, will add new table, commentmeta, to database for EACH blog in WPMU install. So if you’re using trac for BP, might I suggest, you also test WPMU 2.9 trac now in mirror install if possible, before many blogs have been installed in your current set up. Less hiccups with fewer number of blogs.
My 2 cents