thats because it updates packages and the thing that seems to be breaking it is the qt package, you just have to reinstall a couple programs and you are good to go again. I can't remember what packages they are off hand.
I did the same command - kdeinit failed, reinstall like 4 programs and was good to go.
If one knows what to look out for you can do updates perfectly safe, that is why it's stressed over and over on the forum and in irc not to do updates unless you know what you are doing. I know this isn't what people want to hear, but it's the truth. Gentoo breakage is easy to do. If it works don't mess with it. Update slowly and carefully - do a bit of research on packages to be updated. It's been mentioned before that the glsa will break kdeinit.