I've had this problem for awhile now. After my machine has been running for a few hours, I start to see colored lines (red/yellow/green usually) around the edges of large objects (people, trees, buildings etc...) that get larger when there is a lot of movement (moving the camera around, or the object is just moving fast). This happens in games as well as watching video on the web or iTunes. I thought it might be a problem with my video card (GTX 285) but when I upgraded a few months ago to the GTX 580 the lines still appear. Rebooting seems to help but after a couple hours they reappear.
I've got 3 Acer GD235HZ's and it happens on them all (bought over time, not same batch) so I don't believe its a problem with my monitor. Also I have a linux server and a Mac and watching video on either of these doesn't produce these lines. I'm using dual link DVI cables going to each monitor (2 in use by PC) if that matters.
I'm up to date with my drivers. If anyone has any ideas or knows a solution I'd be happy to hear it. Thanks in advance.