Did you notice that we just had a stable release of Chromium? It's a great news, and www-client/chromium-5.0.375.55 is now in portage.
My plan is to start the stabilization process soon, to move it from ~arch to arch. Before that happens though, I'd like to ask you to help testing this new package. Please try emerging it on your system and report any problems you encounter to the Gentoo Bugzilla. Note that the bugs are really getting fixed. For example, here's the list of fixed www-client/chromium issues.
If you're running a stable system, you can keyword-unmask it easily:
echo "=www-client/chromium-5.0.375.55" >> /etc/portage/package.keywords
emerge -av www-client/chromium
For more information about unmasking packages, see the Gentoo Handbook.