My blog reading habits are a bit different from most. I only subscribe to two or three blogs and for the remainder of my reading I subscribe to topics through the various blog search services. In the last year, my feed inbox has gone from about 20% spam blogs to about 80% spam blogs.
I read feeds in my IMAP account and so I've got Thunderbird's powerful spam filtering, plus Message Filters and that helps me keep on top of a lot of it, but it's still getting pretty bad.
What's happening lately more than it used to is persistent and massive blog spam floods that are little more than jumbled text from real blog posts mixed with popular search keywords. Most of the time it's not long before I find that a persistent flood is coming from 20-30 blogger accounts and I can deal with it through a set of Message Filters on the site's URL.
Still, it's a pain in the ass and Google Blog Search and Bloglines seem to be the worst (out of my 10 or so blog search services.) Are they just not interested in keeping those indexes clean or have the spammers really beat them?