I noticed that people get annoyed by frequent updates of www-client/chromium (it takes a lot of time to compile), and someone even said something like "don't inflict those updates on me", which makes it sound like an update is something negative.
In my opinion a very active upstream is a good thing. Usually we don't need to keep local patches too long, because they just get included in the next dev channel release. We don't need to wait too long to see whether a particular bug was fixed, and so on. Also, most updates in the stable channel are security fixes.
On the other hand, I understand the frustrations caused by long compile times. There are various theories about bundled libraries in Chromium causing that, but I don't think they're accurate. We use system versions of most libraries, and there is a work in progress to remove few remaining ones. The largest pieces are WebKit (open-source HTML rendering engine, also used by e.g. Safari) and the browser itself. You can try compiling qt-webkit or webkit-gtk to see how long they take to build.
Okay, so what's the solution?
I tried to support a www-client/chromium-bin package in Gentoo, but it had quite a lot of problems, and is now masked for removal (and should get removed in just few days). Just to give you a few examples: bug #304527, bug #335101, bug #347175, bug #349249, bug #356609.
I think that a solution that may work for many people is using a Google Chrome package from some overlay. There's nothing to compile, and the download is about 20-30 MB. Why an overlay and not portage tree? See bug #272805, comment 170 for a pretty good explanation.
I tested www-client/google-chrome from belak overlay, and it seems to work (please remember that unofficial overlays are not supported by Gentoo in any way, and any problems should be reported directly to the overlay owners; the overlay may contain more ebuilds than just google-chrome, so don't be surprised by that). It's easy to install with layman. Make sure you have "mercurial" USE flag enabled, and then:
emerge -av layman
layman -a belak
echo "source /var/lib/layman/make.conf" >> /etc/make.conf
emerge -av google-chrome