I thought that the wonderful mouse button configuration programs, btnx and btnx-config, were both available in the Ubuntu 12.04 repositories. Well, apparently they aren't? [But they were for a time, and I don't know why they were removed.]
UPDATE: For those running 12.10, I have posted a slightly dirty but workable solution here. Hopefully someone will take my patches and make a PPA of btnx. I'm looking it myself but it feels like a lot of work.
btnx is the best mouse-button configuration program I have found, bar-non, in any operating system so far. (I've tried others but they are either too complicated OR don't do the simple things I wanted.)
To install btnx in Ubuntu 12.04 (assuming Ubuntu doesn't fix this glaring error themselves), just download the appropriate version for yourself:
For example, you would want to download this sort of file (if you were running 64-bit): btnx_0.4.11-3ubuntu2_amd64.deb
Make sure to get both the main program and the gui. After you have downloaded them, you need to install them. You may be able to install them using a graphical program, and then resolving the dependencies later. My approach was a little different and slightly more advanced but I knew exactly what was going on.
I opened a command console window, changed directories to where I had downloaded the btnx *.deb files, and ran the following command:
sudo dpkg -i btnx*
It proceeded to partially install the programs, but had a dependency error. I then ran this command to fix the dependency problem:
sudo apt-get install -f
In my case, this installed the dependency package 'menu'. Then btnx was successfully unpacked and installed. Now, btnx tried to auto-start its service after this but had an error. However when I manually ran the program manually through the applications menu, it opened just fine. I fed it my previously saved config files and everything worked.