The main difference between Arch and Gentoo from an installation point of view is that Arch generally doesn't include configuration in its packages. So for every package you install, you have to manually set up the config before it will work. Gentoo often has the config set up for you. In my experience, this often makes Gentoo faster to set up than Arch, even though you are building all the packages. I actually moved to Arch, though, because the lack of configuration means that there are less dependencies in Arch (if you want optional dependencies, you have to configure them yourself). For me, this made Arch a bit more flexible. You can also build all your packages by hand using the Arch Build System (ABS). The one thing from Gentoo that I wish was in Arch is the license manager. I liked the idea that it would keep track of the licenses that I agreed to and warned me if I tried to install a package with a different license.