Had been playing around Beagle for a while. Its still in its alpha stage but seems to be ok for everyday use. One feature that it should have is the ability to stop the beagle daemon when the laptop is on battery. Continous disk activity doesn't make your battery happy. Wonder if Apple's Tiger spotlight feature has this feature.
One of the notable feature of Beagle is the Gaim plugin. I find it useful to search for previous online conversations. Provided of course that you enabled logging for Gaim.