Very fast but who cares about a millisecond? Reliability is most important. If you get this drive, expect to use your backups sooner than expected or lose your data!
Mine died after 8 months use. Will not go Samsung for hard disk again. Warranty = 1 year (or is it 18 months?) compared to Seagate's 5 YEARS!
That says it all for me. That and the fact all my old Seagate drives are still working and this one is dead in the water.
For a little extra you can get a faster Seagate 32MB cache which as well as being more reliable is faster to boot (5.9 in Vista).
EDIT: Samsung have a longer warranty than I thought, although still not the 5 years of Seagate. Have just used Samsung's returns company REXO who sent me a replacement in 3 days. Very fast, efficient and easy to do. I have to say I'm a happy camper again, and I'd consider buying Samsung again for some purposes. That said, I'll be making backups a lot more often than before, and not just with Samsung drives, and it will take a lot to beat Seagate's 5 year warranty.