It's probably too late to get this into the next release, but I thought I'd submit it for a future version (or someone could produce a hack or plugin, I guess).

I was just remembering a comment someone made on my blog several months ago, but I have no idea to which post it was made (it was an off-topic comment). I started to try to use the built-in search engine to find it, but then realized it does not search comments, only posts.

It would be nice if you had an option there to search only posts, only comments, or both. Sometimes people make interesting comments, or I comment on my own blog, and that information is not indexed for searching.