LWN is reporting an issue with the Intel e1000e driver in the development kernel (2.6.27) that could leave your network card permanently damaged.
At this point, Gentoo provides this version of development kernel with the git-sources package. This issue apparently does not affect network cards using the e1000 driver. So, if you use the e1000e driver please do not install or use git-sources. As soon as a patch hits the mainline git tree I will update the package version which includes the fix.