I've just tried Gentoo on my main desktop box for four months. Initially I thought it was great, however with time my enthusiasm started to fade. Portage broken due to a developer checking in a bad version, perl version ping-pong and a lot of other annoying quirks that could all have been avoided.
As a long time bsd user the portage implementation is nice in a linux context, however Gentoo as a whole just did not get there for me. My main gripe being that you spend more time trying to keep the system coherent and ironing out the creases than actually using it. Ok that's fine if you want to learn about all the internals but if you've already been then it quickly becomes tiresome.
On the good side Gentoo had a few novelties I found quite interesting, an innovative init system in particular, automated etc updates, use flags and a good user community.
On the downside I found Gentoo sits uncomfortably on the fence when deciding between freedom of choice to install what you want and a minimally stable base system. In my four months of use, I had about one month where all the elements of the base system could be considered coherent and functional without needing an upgrade of some sort to a major component. Another strange quirk is that the vital portage depends on python. Nice idea but if portage or python break then your in trouble. Would be much more reassuring to have a static portage.
What finally drove me away from this distribution however was the general quality of it. A lot of the ebuilds are little more than quick hacks and not a genuine port. It works on the developers box, fine lets release it to the world. Testing policies and quality control seem to be less of a consideration than getting things out before the other distributions. That's fine if you judge the quality of a distribution by how much of the latest eye candy and gimmicks you can install. Personally I tend to judge more by the quality of how a system is integrated, developed and its code base. I found Gentoo to be somewhat lacking in this department. It just does not ooze the quality coding of debian or bsd flavors. Perhaps that will come with time. However having seen the way Gentoo evolved over a fair period, I have a few doubts. The ideas are great but I just could not take the implementation seriously.