Sideline is an Adobe AIR desktop application built with the Yahoo! User Interface Library (YUI) that allows users to create and group custom queries by topics of interest, as well as view topic trends. Very nicely done. Am looking at at how the advanced search works at the moment. Looks very easy to build up an seems like it might be the perfect app for a lurker or follower who doesn't post much.

http://sideline.yahoo.com/