This weekend I tried out Exherbo Linux. It was recommend by a friend of mine, so I gave it a try.
First of all: Exherbo Linux has a great mascot. I really like it, and I like that a distribution is brave enough to use it as a mascot ;-)
Exherbo Linux is a source based rolling release distro. It is in many parts very similar to Gentoo. It uses Paludis as a packet manager, which was created to replace Gentoo's emerge and portage. Therefore I liked their approach. Also you have to do a lot of work by hand to install it on your box. So there are really many things like in Gentoo.
What I didn't like: the lack of documentation and tutorials. Yeah, I know about the freedom of choice and all, but some tutorials and documentation would have been very nice. It took me nearly a whole day to learn about Dracut, the way it handles full disk encryption and keys on external media, and I had to dig to the source to understand it. Also the quality of the packages is sometimes poor, worse than in Gentoo. You have to be willing to repair things by hand if you want to use it.
All in all: a nice approach. I like it. But the lack of documentation is really a serious problem. You have to be willing to invest a lot of time to learn things by yourself if you want to use it.