metasploit-3.1 is the last package in gentoo-x86 that requires rails-1*. Rails 1.2.6 is very old, no longer security supported and the ruby herd *really* wants to get rid of it. So, please consider stabiling 3.2_p6750 (added Jul 08) and remove 3.1 after that. Thanks.
Arches, please test and mark stable: =net-analyzer/metasploit-3.2_p6750 Target keywords : "amd64 ppc x86" -- as approved by pva on IRC
amd64/x86 stable
Alex, I think you can remove the old ebuild now.