We do something similar to this at Leanpub (http://leanpub.com): a blogger can enter their blog RSS feed URL, we import the blog, clean the HTML and put it into a Dropbox folder. The user can then click a button and we publish to PDF, MOBI and EPUB.

The part we don't do is the automatic scraping of related content, and the reason we don't do it is that chances are you don't own the copyright to it. (We don't even include blog comments, since we're not sure about the copyright issues there.)

We're bootstrapped and doing customer development, so any feedback would be welcome...