I recently purchased a 13" Unibody MBP, with the 250gb HDD. Im looking to upgrade that to a 640GB HD, and I have been looking at newegg. They currently have 3-4 of them up there, and 2 of them (The WD and the Samsung) have reviews saying not to use it in the MBP, because the Hard Drive will constantly spin down and go to sleep. Im a little worried about buying one as I dont want this to happen. Id like to find a Hard drive that will work perfectly in the Macbook pro and not have the "beachball" issues as they call it. Ive been looking at the Seagate Momentus, which the guy at bestbuy told me was made specifically for the Mac (even though it says Mac + PC on the box, as do all of the other ones.) I dont really trust the word of some high school kid from best buy, so Im wondering if anyone here has installed this drive, and if so, how is it?