When Google blog search launched in September, it only indexed blog posts from about mid 2005:
[...] Since Blog Search indexes blogs by their site feeds, it will only include items that have been posted since it started indexing a given blog. For most blogs, that will be around June 2005, or the time at which you submitted your blog for inclusion. We are working on ways to include older posts as well.
Well, I've noticed recently in the RSS feed I set up to track my name that I'm increasingly getting feeds from blog posts earlier than June. Looking just now, I see a few from back in early April.
They must have found those ways.
[EDIT] A post dated 30 January just showed up in the feed. Clearly things are moving along with Google's indexing.