Coolest feature: the ability to fashion a keyword/category query into an RSS feed across all Microsoft blogs. If you're only interested in certain things (and personalities be damned!), you can sign up for the keyword feed. (And if you're really serious about losing personality, try running it through a text-to-speech program afterwards, or removing all the adjectives).
Bit that looks like it needs work, but might not actually need work: The categorization gets pretty coarse (for someone that plays in the Windows space, having “Windows” as a category is a little on the “too general” side of the happy fence), and in some cases blogs aren't (yet) categorized appropriately (I'm sure we'll work on that) - but you can easily overcome that by throwing in a keyword or two when picking a category. Heck, my category titles look like blog titles to the categorizer(TM), so I'm going to have to edit them a bit now!
Tim's one of the people behind the project, and he's interested in your feedback, so drop him a comment!