John Battelle (and others) seem to think that Blogline's index of 280 million blogs posts is one of it's most valuable assets.
While there's no doubt that much data is worth something I doubt any search company would find it very valuable. After all:
- They already have the data in their main index (in the form of the pages it came from) and (more importantly)
- Blogging (and related applications) is concerned with the most recent, up to date data possible.
Old blog posts do add depth, but nothing like the amount a real search engines index can add.
On the other hand the detailed data about a million user's interests, and information about who created what content…. that is something worth paying for.