This blog post has some valid points:
I firmly believe in updating server software only when you need to. If you don't need new features, and things are working, why change anything? If you update anything you will undoubtedly need to update configuration files. You will need to fix things that break in the upgrade process... This is hard with Gentoo. Gentoo wants you to change a lot of stuff. It wants to be bleeding edge.
I agree 100% with author. I always use and recommend RHEL or Debian Linux for production server. Other choice includes FreeBSD or OpenBSD.
What do you think? Do you run Gentoo on a production box?
Update: Check out this post by Josh - Why Gentoo is a Great Server Distribution (a Rebuttal)
PS: Someone is looking for Gentoo Admin .