I have a Non-Unibody MBP 4,1 Penryn and recently installed a Momentus XT HDD. I have to say, it most definitely made a difference. So, if there are any of you out there contemplating getting this hard drive or are tired of a slow mac, I recommend this. The install really wasn't that bad. I used CCC and everything worked perfectly. I was getting very frustrated with my nearly 5 year old MBP- lots of beach balling, slow start up, very slow app launch, and this solved everything, at least for a while. This will definitely hold me off until I can afford a new MBP.