Upgraded today to 12.10 and then to 13.04 (which I'm currently using). After the upgrade I noticed that mouse clicks are not always registered. Turned out that I have to "hold" a mouse button longer for click to register.
Touchpad works ok.
Went to Mouse Settings - nothing I change fixes this behavior. Tried "Test you settings" - when I double-click as usual, "single click" is shown. To show "double click" I need to press on mouse buttons a little longer.
UPDATE: When I change my primary button to "Right" instead of "Left" - both buttons work correctly. Left click instantly brings up context menu - no need to hold it. Mouse is ok - no lag in Windows.