I have a Momentus XT 500 GB that I purchased from Amazon in August 2011 for use with my "Late 2008" MacBook (MacBook5,1). The XT came with SD26 preinstalled. I installed SD28 when it came out (about a month of having the drive), as some users were reporting increased performance. Didn't really notice a difference. It seemed to be working fine (snappier than the stock MacBook HD for sure) until about a week ago, when I began to notice a BIG decrease in system performance. Ran a SMART status and everything is fine. Did an Xbench test and my sequential write score was 86.66 (so-so for this model HD compared to other people's scores on the forum), and 22.26 for the random score. Those are a tad better than the average HDD, but not nearly as fast as it was. More importantly, the system feels MUCH lagger. I used to click an icon on the dock and it would *maybe* bounce for a second, but would open so fast I couldn't really count a second. Now it takes about 3 seconds. Also, I'm getting beach balls all the time, and in general it just takes longer to open files (especially large ones). To rule out a possible OS problem, I've wiped the HD clean and re-installed both Snow Leopard and Lion (Lion being a bit better but still not as good as it was when I first got the HD). I am positive it is NOT due to the OS, and even if it is, I want to be sure my HD isn't defective. I was reading on the Seagate support forums that it might have something to do with the ADM on the XT models. SD28 was supposed to address this, but who knows if it does for everyone. Moreover, I *believe* there is a bigger issue with Mac incompatibility (specifically MacBook's and MacBook Pro's). I read that a LOT of the problems with the Apple crowd stem from MacBook (and MBP) seemingly being incompatible with the XT (thought I don't see how that could be). Seeing as how their "SeaTools" (required diagnostic tool to send a bad drive in) only works with Windows, and that Seagate does not provide any diagnostic tools that are Mac-friendly, I'm inclined to believe that it IS indeed more of a hoaky "not the best for Mac" thingies (as much as my techy soul thinks that software and hardware should just be able to work together). I even tried running Seatools via Windows XP SP3 (Boot Camp partition AND via Fusion), and I couldn't run the application. Got some random error I forgot by now. So i'm poised to send this in and get a replacement ASAP, but as I was filling out the RMA, i noticed the Seagate text, "Please do not return a healthy drive. Seagate reserves the right to return a good drive back to its owner and to charge for all associated shipping costs." Dang. Anyways, I was curious if there are any other XT users out there having a similar problem? I would go to the Seagate forums (and believe me I have), but the Seagate forums are really terrible to sift through -- mostly lots of angry people (which I can understand totally). And angry people are largely stupid people, at least when they're angry, so their posts just cause chaos. And to be honest, I don't care what problems a Windows guy is having on Windows 7, etc. I want to know if any Mac guys are having a bust, and if so, what they have done/are doing to get the old speedy XT back. So that's why I'm checking in here! I mean if this is just what it is... I might have to go get an SSD/optibay thingie and just do that..