I have it for about a week in old Macbook Pro 2.33, i noticed that is a lot louder, than my previous WD Black 320GB (which was exceptional in 7200rpm 2,5" driver, quiet, cool etc, Momentus XT sounds like a quiet fan and i can hear seek sound from about 1m away, still tolerable, at least i know that it is doing something) I never owned a better hard drive than WD black 2,5" and i get 3 of them for PS3 and another Macbook). I dont trust Seagate so well, because i get many of them into hands (im selling computer parts) and many series has got terrible, really terrible firmware problems, heat issues etc... but i still bought it

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Since i have only SATA 150 (SATA I) on this chipset, there is not as big difference as i expected, especially booting up the OSX. I have old instalation and upgrade from Leopard, so i know that it is full of stuff and its booting slower. Maybe its problem with temperature sensors, because is stuck on gray screen for about 15-20 seconds, than it starts to boot. I propabbly shoult reset PRAM and other options. I also have some sleeping problems, but this should be soulved also by PRAM reset...
Great for internet browsing, because all caches from Safari or Firefox loads faster, so no lag after first open etc, great compromise between speed and space. Itunes artworks are loading amazingly fast in 9.1 and almost immediatelly after 9.2 update.
Overally, the Momentus XT isnt as much faster than the older WD Black that i had, in overall performance, but it almost erased some issues that i had about hard drives in every computer, like browser lag, itunes artworks, slow computer performance with rar and zip archive decompressing (i should thank to the 32MB cache). I hope that it will show its full potential next week, when i get i7 MBP... and test it in Parallels and other IO sensitive tasks (how fast the mechanical part is).