Yay. I was under the impression this was going to take till the end of the month or later to be released. It's good to know MS was right on top of getting that thrown out the door in a hurry because it's desperately needed. The MBSA should almost be released in parallel to such service packs that need an updated version.
MBSA is unreliable. For example, it fails to find a well-known vulnerability in SQL Server. It also hides many details of what it's checking, not letting administrators see what's actually going on. Leaving admins in the dark when the tool itself is known to be unreliable is a very bad situation. I haven't heard how reliable it is for XP SP2, but many good admins say it doesn't actually save them any time or help make systems any more secure because of all the redundant manual work still required.