I've had the 3TB Samsung for a month, and I'm finding it a very speedy & reliable drive for use with my MacBook. I use it primarily for Time Machine and for storage of large media files, including HD video, which I can play back from the drive without lag or stutter - even while a Time Machine backup is going on in a separate partition on the same drive.
The only negative point is that it does have a slightly annoying spinup whine compared to other drives I've used, as well as an audible tapping noise when accessing. I don't believe it's faulty. These sound like the typical noises that a hard drive makes, just a bit louder than I've previously encountered. It's virtually silent when running without accessing.
I scanned it for bad blocks as soon as I received it (none found).
If you're planning to use it with an Intel Mac for Time Machine backups or as a startup disc, remember to change the partition scheme to GUID, as recommended by Apple, before you do anything else. You can do this in Disk Utility.