You can now filter posts by Category on the blog. You can have any number of categories, a post can be assigned to multiple categories, and you can completely disable a category (this doesn't disable the posts, but only keeps the category from showing up in the nav).

All in all it works pretty slick, working in combination with the week/day/month filter, so you could show all Blogdev posts for the month of September or the second week of August. It required doing some custom work on the keepURL functions that MM uses to keep Querystring parameters, but it's worked out pretty good if I do say so myself.