I've been idly looking for a solution to the blog backlog problem. Lately I've seen others looking for the same thing, so I'm expecting a fix within the next few months.
What's the backlog problem?
The backlog problem is discovering a great blog, but reading only the most recent posts. That is, after all, how blogs were designed to work. Problem is, there's a lot of great stuff in the backlog. I'd like to read that too - the same way I read my other blogs.
What I want is a special feed for every blog I read that's the 'random post feed'. It could be generated by a WordPress extension for example -- it just has to be integrated with the blog's database and publish 1-2 posts a day. 
Any day now ....
 Google Reader could have done this because Google kept old posts around, but nobody else is going to keep billions of blog posts in an archive. The RSS feed for backlog posts has to come from a random selection of all past posts -- say 1 random selection a day. I've seen mention of using Yahoo Pipes to do something like this, but Pipes can only randomize the urls exposed by a feed -- not all past posts.