KDE has it's own version of Desktop Effects, some say they perform better than Compiz. To install them in Ubuntu all it takes is a trip to add/Remove software and search for Compiz. As far as whether Compiz will work with the new KDE Desktop effects, I'm not sure if that's possible. I ran Compiz in Debian Sid back when there was only KDE3.5, but, that was before KDE4. I would tend to think there are conflicts between the two.

Anyone else here try using both?

Yes, Ubuntu with KDE is Kubuntu, but the question and answers are the same, will Compiz conflict with KDE desktop effects? I haven't tried, but I speculate it would be a problem.

Ubuntu with KDE is called Kubuntu.

The KDE4 desktop effects are basically the same as compiz, but easier to configure. If you attempt to install the compiz packages on KDE4 you will get conflicts that will result in instabilities and/or mis-configured files.