From Top Ten Web Design Mistakes of 2003 (Jakob Nielsen's Alertbox)

"It used to be that Web sites offered one or two things. Now it's common to find sites with thousands or millions of items. Wonderful, but that means that item listings are often very long and hard to use.
One of the main usability guidelines for category pages is to let users winnow items according to attributes of interest. To "winnow" a list basically means to filter out elements that don't meet specified criteria, leaving a shorter list that's easier to manage and understand. "

Sounds like a job for faceted classification! Dooo do do!

Looks like I complained too soon... movabletype.org: News announces that 3.0 will feature "Comment registration. As a response to both comment spam and to the increased usage of Movable Type on large community sites, we'll be adding the option to restrict comments to registered users. "

the question of whether the underlying architecture is stable and scalable is still an open one, but at least this accursed spam might be stopped.