I switched to Paludis yesterday. For those who don't know what Paludis is, it's an alternative Gentoo package manager, or a Portage/emerge replacement. It has not all been smooth. I had to fight with it for a while, re-installing a bunch of packages that thought they depended on an installed package that no longer existed. I think this was because Portage left some cruft around that made it think that. The problems were mainly to do with kdelibs-3.4* (which a lot of installed packages thought they had a block on) and with guile (which moved to a new category but some packages weren't aware of the switch). Re-installing worked in most cases.
The other wrinkle was that the portage2paludis.bash script that I used according to the migration instructions didn't bring all my repositories over, including my /usr/local/portage and a few others. The second annoyance was that a few repositories didn't have profiles/repo_name and profiles/categories files in them (which paludis requires) and this causes a bunch of warnings about how paludis is "faking it." I finally got it to the point where I could do "paludis -ip world" and I got no warnings and no errors.
The only remaining problem is that the gentoo java packages are mostly unusable with paludis because none of the hooks in the java gentoo eclasses get installed into paludis' hooks system (and paludis doesn't call the hooks in the java eclasses). Apparently the Gentoo Java team was "abusing the [portage] hooks in [their] eclasses." They should be installing the hooks into the paludis hooks directories. Paludis hooks are similar to subversion's hooks system. They allow you to do a lot of fancy things.
Overall I am impressed with Paludis. Running "paludis -ip world" is a lot faster than "emerge -uva world" or "emerge -uvaDNt world" but more important than speed is that it was designed from scratch, without all of portage's warts and messy hard-to-change code. In a way, paludis is to portage what svn is to cvs. You can read all about the differences between Paludis and portage here.
One more thing happened yesterday, that was a little bit scary. I tried to reboot to try out a new kernel and I noticed the "reboot" and "shutdown" commands were no longer there. I rebooted anyways but hitting the reset button but the system wouldn't load, it stopped right after the kernel was done starting up. It turned out Paludis had uninstalled sysvinit when I ran "paludis --uninstall-unused" and I didn't notice. Reinstalling it fixed everything but I got really scared that the reboot and shutdown binaries were missing due to dataloss.