A lot of the binary packages in portage are linked against libstdc++.so.5 without listing sys-libs/libstdc++-v3 as RDEPEND. These binaries stop working after an upgrade to gcc-3.4.4 because libstdc++.so.5 will be removed from the system. This concerns notably: www-client/mozilla-firefox-bin and media-video/realplayer. While these are the packages that I noticed and have installed on my system there are probably a bunch of other packages that require libstdc++.so.5 without explicitly listing it as an RDEPEND.
*** This bug has been marked as a duplicate of 84961 ***