I recently upgraded to KDE 3.4. I had been waiting for the gentoo folks to unmask it (or rather, promote it from ~x86) but I got tired of waiting. I found a nice script called "gimme" here . This script will add a package to /etc/portage/package.keywords effectively marking that package as ~x86 (or whatever your arch is) so you can emerge "experimental" packages.
The sad thing about this script is that it does only the one package. I had been running the monolithic KDE ebuilds for 3.2 and wanted to switch to the separate ebuilds. There were about 202 dependencies that I'd then have to call gimme for. So like any good UNIX/Linux type, I scripted it. I extended the gimme script to recursively resolve dependencies until they have all been resolved. Here is the script for what it's worth. It's been functional for everything I've used it for but I can't guarantee it won't be flaky in certain circumstances. I hope you find it helpful.