I'm on a 2010 15" Macbook Pro and also have this problem (exclusively with Safari). There's absolutely no way it's a hardware problem since it never occured until Safari 6 and doesn't happen in any other software. It's noticably worse with dynamic objects (I see it freqeuently on one of the web-based tools I've built: http://aweathermoment.tumblr.com/metars) and while I've been able to alleviate the problem at times, there seems to be no real fix. Playing with gfxcardstatus can help, but it always seems to return after a short while.
If anything, the fact that gfxcard status can help suggests to me that the root of the problem lies somewhere in Safari 6's new accellerated page rendering engine. Hopefully Apple can squash this bug quickly. Remember that while this is the official Apple Disccusion Boards, it will never hurt to send the Safari team feedback and directly letting them know about this bug: http://www.apple.com/feedback/safari.html