I'm about to upgrade to MacTeX 2011 by downloading the entire installer as described here.
So how do I uninstall MacTeX 2010 so that my system is as clean as though I haven't actually installed it?
First you install MacTex 2011. In the pref system, you can select your TeX distribution. If you are happy with MacTeX 2011, you can search MacTeX 2010. In the finder you use the item "go to folder" with 'shift cmd G' and you type : /usr/local/texlive.
You see three folders :
You can now put the folder "2010" in the trash, you need to give your password at the system to do this !