The KDE site is probably a better place to begin, as the others may be a little overwelming at first.. I just thought I would mention them again, as they show alot of great features!
I too switched to KDE4 early on; the first few days took a bit of adjustment, but overall I have been very happy with it... I've been eagerly awaiting the 4.4 release (more than any other) since watching those videos. I love the idea of being able to add disparate applications as tabs in the same window. The auto-resizing of windows when pushed to screen edges will also be a useful feature.
In previous PCLOS releases of KDE4 tex had disabled nepomuck due to poor performance.. I think I saw on his twitter page that it is now more functional and will likely be enabled on the 2010 release (..for those not familiar with it, it is the live search & filter engine used in many parts of KDE4; it should offer functionality similar to Google Desktop -- and more)