I had some problems with my iMac G5 recently, but I have Apple Care. I think the problem is fixed, but wanted to share my story. I was having problems with the computer freezing and bad pixelation of the screen. Sometimes, the startup screen looked like a video that was being rewound while playing (horizontal bars/stripes, "snow", etc.) I read some of the older threads here and found some similar problems and was worried that it was the midplane. The Apple techs had me remove a memory stick that was installed at the time of purchase. I had it up to 512 MB. It turns out that I had two different brands of memory. The stick that came with the computer is a Micron. The second was a Samsung. The tech support guy had me remove the Samsung stick and everything is working fine again. So, does brand really matter, or is the Samsung just a faulty stick by coincidence? Either way, I was told to take the stick back to the store and get a refund or another stick. I may get the refund and put it toward something else, as I don't see the difference in cutting my memory in half.