Here I can see that skype is stable for amd64: http://packages.gentoo.org/package/net-im/skype
But Skype is masked at 64bit profile.
$ eselect profile show
Current make.profile symlink:
Because skype is a 32 bit application which requires multilib to run on amd64 systems.
What he said ;)
It is some binary blob of proprietary mess from upstream.
%% file /opt/skype/skype
/opt/skype/skype: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
dynamically linked (uses shared libs), for GNU/Linux 2.4.1, stripped