I had been using libjpeg-turbo with x2go for well over a year now. Initially I just replaced libjpeg with it by installing manually then creating a softlink but as far as I know libjpeg-turbo replaced libjpeg in Ubuntu a couple releases ago and *I believe is now the default.
<goog_1060864767>* https://blueprints.launchpad.net/linaro-ubuntu/+spec/o-libjpeg-turbo-integra...
At least for Ubuntu 11.10 there you can see the launchpad entry for it here:
http://packages.ubuntu.com/en/source/oneiric/libjpeg-turbo
You might check with Debian to see if libjpeg-turbo hasn't already replaced libjpeg there as well.
Brian