This happened to me very early on--about two weeks after purchasing--and I took it back to the Apple Store for a fix. If they couldn't fix it, I told them I wanted to return it without a restocking fee because it's pretty much unusable when on battery power. It's not just Safari and Mail (or anything based on WebKit). The glitches show up in the OS X GUI, such as when you're installing something. The progress bar flickers. At least, that was my experience.
I'd installed an SSD when I got this because I'd purchased one preemptively when it was on sale. I installed it right away and so when they found out I put in the SSD they wanted to test the computer without it. Of course, being so lucky, it worked fine when they put the 250GB stock hard drive back in. Two weeks later? The problems are back. I'm headed back to the Apple Store tomorrow to complain.
What's ridiculous is that I said it couldn't possibly be an issue with the SSD because the SSD is faster than the stock drive and they were trying to tell me it was because it couldn't keep up. Also, I went around the store with them and we found another MacBook with a stock hard drive that exhibited the same problem! EXACT same problem. They insisted it was a different issue. Honestly, I was happy enough that the problem was gone so I didn't care enough to keep fighting a hopeless battle. Now that the problem is back I am really, really angry. I mean, they spent the whole time trying to get rid of me and it's not like I was mean. I make a habit of being as friendly as possible when I go to those stores because I know how far angry people get at the Genius Bar. Lord knows I've been there enough to see these arguments play out. I've also worked in technical support and I know that once a customer gets angry, I don't want to help them anymore.
Not that I expect to solve this by tomorrow, but I'm trying to find some definitive proof that it's the 9400M. I mean, that makes the most sense. On the other hand, it's entirely bizarre that it disappeared for two weeks with a fresh system install. How is that possible? I mean, obviously we're not going to start re-installing OS X every time the issue arises. That's a little ridiculous. But still, what's the inciting incident here? What happens at two weeks that causes this issue? I duplicated the SSD to the stock drive so the data was identical. It's not something I installed. I didn't give the machine one moment of rest so it's not like it cooled off for a few days and regressed back to working form for two weeks (which is sort of a silly idea to begin with). I think the most likely answer is that the machine has a bad graphics card, but that doesn't explain why a fresh hard drive solves the problem.
Or maybe it does. I don't know a lot about how OS X works under the hood, but I know a little bit. I know Safari, like any web browser, caches everything. Additionally, OS X's virtual memory caches tons of crap to the hard drive regularly. The swap files it creates are enormous. Maybe there was something to the silly answer the Genius Bar tech gave me. Maybe the hard drive, in a round-about way, isn't keeping up.
Bear with me here. Clearly I'm reaching, but with no help from Apple this is about all we've got to do. Because the batteries in these new MacBooks and MacBook Pros have lower capacities than their previous models, more efficient power management becomes very relevant. Both the CPU and GPU are more efficient on their own, but I imagine that when on battery power there is going to be some serious throttling whenever possible. The errors we're seeing look like the graphics card is having trouble keeping up when redrawing areas of the screen. We're seeing flickering when watching videos or when high frame rates are present in other operations, and then we see page tearing when scrolling smoothly through web sites. Notice how it doesn't happen when just jumping down the page? So I imagine this is more of a power management issue than a graphics issue.
But to get back to the hard drive, it seems to happen with applications that cache more than others. It's not that the hard drive is the issue, I think, but that the machine is relying on cached files in an effort to keep the computer cool. The hard drive is going to generate less heat than the CPU and GPU, so why not throttle them both and rely on the caches as much as possible. This would make for slow redrawing because the display looks like it's trying to use old information when it clearly should be updating to what's new on the screen.
Obviously there are some holes in this idea. I'm not an expert with OS X and UNIX. I just have some surface knowledge and want to figure out what's going on here. I'm hoping someone more knowledgeable can chime in and help make more sense out of all this.
If not, we can still all gather data and call Apple as George suggested. I'll be hammering at them tomorrow.
But one thing I noticed about these new machines is that they run considerably cooler than any other Apple laptop I've ever owned. The fans rarely run. It seems like heat is hardly an issue. So I have to ask, is that consistent with the rest of you? Are your machines cooler than past models? I'm curious if the machines with this issue tend to run cooler than the others, or if it really is a benefit of the new hardware.
