This is my case.
I have been experiencing this random image/graphics problem after I upgraded on Mac Lion. I am quite disturbed if this is a video graphics and hardware problem or just because of Lion not being stable for Macbook Pro 13" mid 2010 (Intel Core 2 Duo 2.4", Nvidia GeForce 320m) . I cannot recall having this issue when I was on SL though. So guys let me know if you have encountered this issue as well. My unit is still on warranty, but I don't have time yet to bring it to Apple Ctr since I mainly use my Mac for work purposes.
So here it is, for some reason, when I'm doing multi-tasking especially on browsers, I tend to scroll too fast and switch on multi-tabs (which I think can be normal). Randomly, I see this pixelated graphics, sometimes black or any background color I'm on. Then when I move over the mouse and just scroll, the pixelated and weird images will went away.
With that, it doesn't freezes up any application I'm on. But it just keeps popping up when I'm on multi-tasking. I also realized that this usually happens whenever I'm on a browser. This doesn't really happen when I'm on different applications especially when playing movies.
So I was thinking to maxed out my RAM to 8GB since I heard that Lion consumes a lot of memory and I was getting a lot of beach balls. I was too happy since my Mac Lion is running smoothly with all applications I use. All I thought I won't encounter the problem after the RAM upgrade. But still. It's still a frustrating issue.
Also, I'd like to point out, when this issues pops up, the weird images only displays on the browser section, not on the whole section of my screen. I mean, haven't seen it appearing on Menu bar and on Dock, just on the browser application. I've encountered this issue on Chrome and Opera. I don't use FF & Safari though.
I am attaching a screenshot.
http://dl.dropbox.com/u/14420357/grahicsscreenshot.png