Briefly, Kevin just pinged me to tell me about Spinn3r - a TailRank product. The pitch: TailRank invested heavily in building a robust blog spider. Through an API, the data that this spider gathers (and filters) is now available for others to create application with. Customers are already signed up to tap in to TailRank's crawl of a million spam free feeds.
It will be interesting to see how this pans out. The service provides a starting point for any blog data based applicaiton. However, when extreme realtime is important to the application, Spinn3r may not offer sufficiently fast updated simply by being another cog in the machine. Interestingly, the homepage has a couple of stats on it - one being 25k posts acquired per hour.
Kevin's a smart guy, so following this will be very interesting. The blog post is here.