This is 12.04 default desktop (unity). I set it to focus follows mouse, and changed the menus to be on the window. This worked for a while, then some unknown even, maybe an upgrade maybe some other ...
When I do a single click, my computer (with Ubuntu 12.04) acts like it was double click. I think it happens in ~50% of cases. It happens with all the program I use: browsers, file manager, terminal ...