I upgraded to Mountain Lion the day of release, so this problem has been going on for quite some time. Either it's getting worse, or my patience with it is getting thinner.
Since upgrading to ML, I've got single stripes of pixels that constantly flicker. They are hard to notice on white and lighter colored windows, but darker windows and colors they pop out very obviously. They're about 100px spaced apart and go across the entire monitor. Here's an image of what it looks like: http://imgur.com/HXjKIcn
Is this at all a known issue? Is it a strange hardware issue that needs actual service?