Well, the only linux distro I've ever really liked, before gentoo of course, was Slackware. Until FreeBSD I had thought package systems were pretty much pointless and were more hassle than they were worth. When I had RedHat installed on my system for a while I didn't even "take advantage" of rpm and went the same route I went with slackware -- installing things from source manually.
Of course, installing stuff manually always leads to confusion and breakage in the system if you don't pay enough attention to your machine and keep things clean yourself. So I don't think I've ever had a given installation of a distro for more than a few months before I felt the need to reinstall.
For some reason I had decided to try out FreeBSD (probably because one of my friends is a real BSD nut and thinks linux sucks

) and I really fell in love with the ports system.
Something that always tweaked me about BSD on a whole was that I seemed to have to run things through a linux compatibility layer. The biggest example was flash; I had to run Mozilla (this was before Phoenix/Firebird/Firefox) in the compatibility layer JUST because there was no opensource flash plugin at the time.
There were a few other things that kind of annoyed me, but overall I was really satisfied with it and thought it was a good OS that met my needs, more or less.
Then i had started hearing about gentoo. I think I essentially wrote it off as a BSD wannabe until I actually got around to trying it (around 1.2 LiveCD, I think?). Even though there was NO installer at all; it was easily the smoothest installation procedure I've ever had, save perhaps Slackware's (this is even including Mandrake -_-).
While it has been about two years since I've used FreeBSD on any of my home machines, portage really does blow ports away from a customizability/tweakability point of view.