So, you want to run Chrome (or Chromium), but you're annoyed by the lack of client certificate authentication on Linux. Turns out, this is relatively easy to solve, there's just no GUI for it as of yet. (As of 12/3/2009.) As far as I know, this only works with the dev and beta versions of the daily build from the chromium-daily ppa on Launchpad. It might work on the official Chrome build, if it works, please tell us. If you're running Debian or Ubuntu and want to install the beta version you can add "deb http://ppa.launchpad.net/chromium-daily/beta/ubuntu karmic main" to your /etc/apt/sources.list and then apt-get update.
The simplest thing to do is go to the usual web interface and follow the instructions to install certs normally. You may also want the CSAIL CA (specifically, the Master CA). If this works, you should be able to skip to telling Chrome to use certificate by default.
Failing that, the next easiest way to install a client cert in the nss database is simply to install it on Firefox; At that point, it should be in the list of certificates you get when you run "certutil -d sql:$HOME/.pki/nssdb -L".
Otherwise, you want to look at the the instructions at Google's page on LinuxCertManagement to install the MIT CA. If you're running Debian or Ubuntu, the short version of that LinuxCertManagement page is to install libnss3-tools, then run "certutil -d sql:$HOME/.pki/nssdb -A -t "C,," -n -i " for both the MIT CA and (if you want it) the CSAIL CA.
Note: If you have a sufficiently new build (r40587 or newer), you may skip this section; Chromium has the UI now.
Here's the last key to the puzzle: Chrome on Linux currently lacks a UI for selecting a certificate, so run it with the --auto-ssl-client-auth flag.
To do this by default in Gnome, you want to edit both Preferred Applications and the Main Menu entry this way links you click on outside of Chrome open this way. (Gnome Do and similar pull their data from Main Menu, among other places.) Once you've done this, you can check your work with this demo page. If everything is working, it should welcome you by name, and tell you that a certificate for your username is installed.