I've installed Kubuntu Hardy Alpha 4 in VirtualBox on my Vista laptop and added the KDE4 desktop (just install the KDE4core metapackage) to see how it was coming along. I must say, I'm impressed by the changes that have taken place so far.
Of particular interest is the extragear-plasma package. This includes a number of widgets, including the KDEtwitter widget (which I really want as Linux currently lacks a decent desktop Twitter client - I like Twhirl on Windows but until Adobe AIR is available for Linux there's no prospect of a Linux version of that), a 3D globe (which won't work in VirtualBox unfortunately as the simulated graphics card is not very good) and a comic strip widget which includes Dilbert (which I really like, and that way I wouldn't need to visit the website every day), Garfield, and UserFriendly.
Here's a picture of the desktop:
As you may have gathered, I'm now thinking I will probably use KDE4 in Kubuntu Hardy, even if I can't get Pidgin to work with it - I've got too many IM accounts anyway, and it supports Jabber so my Meebo, Google Talk and Social.IM accounts will work, as will my MSN one, and that's all I really use.
Anyway, hope you like the look of KDE4!