I plan on buying an iMac in the next month or two, and the low-end model meets my needs. But, I've read about several issues. One, the graphics card: There seem to be errors due to drivers (or lack thereof). Two: I've read that the 20-inch screen has bleeding issues whereas the 24-inch does not. If the graphics card on the low-end model is too risky, then I'd go for the high-end 20-inch, and I'd rather not spend the money on the low-end 24-inch. Should I be concerned with these problems or should I buy the low-end and hope that these issues will be resolved with firmware/Leopard updates? Furthermore, I'm going to upgrade the RAM to 4 GB from Macsales/Crucial/Newegg. Will this void the AppleCare warranty?