I've got a frustrating problem that seems to have cropped up within the last two months or so.
Infrequently, the left (primary) click stops registering with the OS, so I can't really click on anything. My mouse moves around the screen, I can right (secondary) click, but I just can't perform a primary click.
I'm running 10.6.8 on an Early 2011 MacBook Pro (http://support.apple.com/kb/SP619). The click stops registering both on the trackpad and my Magic Mouse.
A restart solves the problem.