> Never, ever, ever, unless you like broken boxes use ACCEPT_KEYWORDS.
As long as you don't go and emerge world with it, you're fine. It's probably insane to use it for glibc and gcc, and I'm not sure I like the way the ~arch keyword has been overloaded to mean "arch specific" AND "unstable" (it masks too much stuff that is perfectly stable), but the worst I've ever seen it do was use a broken ebuild and fail to compile it.
Yes, I have made the mistake of emerging a bleeding edge glibc. It hasn't completely stopped me from occasionally using ACCEPT_KEYWORDS however.