Feedster has many advanced search features most people are not aware exist. Since every search is deliverable as an RSS feed, you can tweak the results of the Feedster database to your content.
You can visit the Feedster advanced search page and search a particular weblog or your entire feed list if your OPML is available online. OPML search is useful for finding that entry you know you saw somewhere but you forget the details. Feedster displays its entire history for a site search while Technorati displays only the past 30 days.
Search your OPML is a lot more interesting to me than site search; you can build your own cloud. If a company wanted to track what its employees were saying about a certain topic they could create an OPML file of all the employee weblogs and subscribe to a search via e-mail.
Feedster indexes feeds (RSS, Atom, RDF) while Technorati indexes HTML. I searched within a few weblogs and found identical results for most weblogs in the past 30 days. In cases such as Scoble’s link blog Technorati has the advantage since the RSS feed displays only 15 entries while the HTML page has a lot more.