Quite a few people have reported problems building icedtea6 or needed dependencies on our IRC channel and as the build is quite resource intensive, Caster has now made binary builds for icedtea6. The package is available via layman using:
layman -a java-overlay emerge icedtea6-bin
The binary package should also make it easier to bootstrap the from source build. The binaries are built in stable chroots so they should run for our stable users too. Please report any problems to https://bugs.gentoo.org with [java-overlay] in the subject. For amd64 users this should be the easiest way to get a 64 bit browser plugin.