I tried the Google's blog search on one of my blogs to see how much they index:what I read that's their current limit, but they will extend backwards over time.
Once they get all my posts indexed this will be a great service for searching my own site. In the meantime, it will be intersting to compare the results of these searches to searching on usenet or the web.
You can subscribe to the search results as an RSS feed, so if there's a topic you want to follow you can add that as a search to your blog reader.
For example, this is a link to a search that finds recent references to Gordon's Notes (as you can see, there are few links!). At the bottom of this page is an Atom feed link that references the same search.
I took the URL from the Atom feed link and entered it in my Bloglines collection. So now when I review my blogs there's an entry that will track any references to Gordon's Notes. Kind of neat, really.