I am experimenting with building www-client/chromium with system-provided V8, the super-fast JavaScript engine. If you'd like to try it, emerge >=www-client/chromium-9.0.570.0 with system-v8 USE flag. By the way, this is not just about web browsers. We have patches for other packages too, for example to make mongodb use v8.
The system-v8 USE flag is masked. Here's how to unmask it (remember, it's experimental, may break, etc, etc):
mkdir -p /etc/portage/profile
echo "www-client/chromium -system-v8" >> /etc/portage/profile/package.use.mask
Please report any issues to Gentoo Bugzilla. Thanks!