I have made a very small patch to the current X Server Configuration HOWTO to indicate the problem with issuing startx after emerging xorg-server instead of xorg-x11. The issue has come up a few times in the fora, and I think it would help to just put a little note about it.
Created attachment 221369 [details] Patch from 1.26 to 1.27 Just adds the information about issuing startx failing if xorg-server was used instead of xorg-x11. Makes the user aware that he or she must firstly emerge some type of window manager or desktop environment.
I updated the X guide some time ago with something similar, so this is fixed as far as I'm concerned.