I stumbled on the Web site BlogBooker, which will create a PDF file from your WordPress, Blogger, or LiveJournal blog. From there, of course, you can publish that PDF file as a book using one of the online print on demand publishers like LuLu.com, or you can just treat it as an e-book. BlogBooker could be a useful tool if you had, say, a blog for a class (online or face-to-face class) that you wanted to save as a final project — and right now I’m thinking about ways of doing online religious education, so this may be one of the tools I make use of.
Though this is only partly-related, I can’t help but think of:
http://fuckingbookdeal.tumblr.com/