The marketers are doing their job, no doubt, but don't believe the hype. Buying a HD that boasts 3.0gb/sec I/O transfer rate, for that reason only, is extremely ignorant at best. Due to mechanical limitations of the drives and of motherboards we attach them to, that transfer rate is a long way from being realized. Even the older SATA/150 technology is yet to be fully capitolized on and taken advantage of. The more relevant numbers we should pay attention to is buffer size, seek time, and rpm as those are far more relevant to the performance of the drive than the boasted I/O transfer rate.
But don't take my word for it, see for yourself