KDE 4.2 was released for Kubuntu on the 27th of January, 2009. This was a big deal because the 4.0 release, typically the "ready" release, was not so ready, and a bunch of nerdy types were not very happy about it. Being a software developer, I understand that a complete re-write, as 4.0 was, will have it's problems.
I use Kubuntu at work 10 hours a day/ 4 days a week, as well as at home, and I took the brave step of upgrading in a production environment, after testing at home first on a similar configuration.
So far, I like KDE 4.2. For some reason my computer was not joined to our domain after the upgrade, so I had to re-join it. And no, I don't use Likewise. Also, my media buttons didn't work for Amarok, but that too is fixed now.
Other than that, I am finding KDE to be quite usable, very user friendly, and quite stable. It is also very pleasing to the senses..well, mostly sight. The "right click" functionality is much better and I can configure the machine using the system settings now! =)
Many tools like KRDC and Kate are greatly improved, as well as many components like the improved KDE menu, which makes it very easy to find and organize programs.
Many of those nerdy types have complained about the direction KDE has gone, and there was a quiet uproar about the 4.0 release. This nerdy type likes what he sees so far. I'll write again as I use KDE 4.2 every day for work and play.