There are tons of great things about kde 4.2 especially for the developers. But there are still lots of features missing, and bugs, some of them glaring. I was hit by one of the more subtle bugs today; konqueror would start with two windows, and then crash. There was no way I could get it running, which was a pain.
Turns out that the file $HOME/.kde/share/apps/konqueror/closeditems_saved was corrupted. Deleting this file fixed everything up.
Now, I really look forward to a new release that fixes the krunner problems and adds dbus functionality to konsole. Then perhaps at some point, an inclusion in ubuntu of the kpilot and a finished akonadi. Then we are about where kde 3.5.9 was when I left it. Especially if I get the apt: io slave back. Sorely missing that one, I am.