Happy as a clam I followed the instructions to get my Kubuntu 8.04 machines upgraded to 8.10 - and with them KDE from 3.5 to 4.1. It was a swift download, about 30 minutes, and I encountered no problems at all with the installation process. Kudos!
After the reboot, though, the problems started surfacing. Most of them were minor, and the only serious annoyance at this point was the changes to knetworkmanager. Once it didn't support WPA (which was an item of criminal neglect), while now it was mandatory to use wpa_supplicant. No problem, once it tried to connect to a network that had encrpytion turned on, you just needed to click on the tiny lock icon to set the encryption parameters.
Why didn't the setup dialog appear on its own, though, as it used to? I spent a good few hours trying to configure wpa_supplicant manually, and ended up setting the encryption parameters purely randomly. To make things worse, there seems to be no way to change the setup once you choose it the first time - going to the setup and then trying to modify a connection yields nothing useful.
That's though only a symptom of a much larger problem, one that ended up costing me most of my support for KDE. To state it briefly, KDE 4 is the worst generation of KDE ever created.