I see that a lot of people here are buying hard drives from places other than Apple because they are cheaper or what not. My question is, does it matter what kind of HD you buy? I know that you can only buy certain video cards for Apple, but is the same true for hard drives? And, what would be a good replacement drive instead of the standard 320 GB? I don't necessarily need huge storage but want speed. I would do the 300 GB 15,000 RPM drive from Apple if only it was not an extra $585. Does anyone have any recommendations?