SATA hype
The moral of the story is that it doesn't live up to it. Almost any given SATA drive on the market right now offers very little or no advantage based over a similar PATA drive.
My conclusion is based on my research into the advantages and pitfalls of SATA and on my own personal experience with my new SATA II (300 MB/sec theoretical maximum transfer rate) hard drive.
The first bit of info I found out was that most SATA drives on the market aren't true SATA drives at all. They are actually PATA drives with SATA connectors and bridge chips built in to interface between the SATA controller and the PATA drive.
A few tidbits on that topic:
With all of that said, what is my new hard drive? I got a Western Digital 120 GB 7200 RPM SATA (sorta) drive with 8 MB cache. And why the sorta? Well, except for some Seagate Barracudas, none of the other SATA drives currently have native SATA support. The cold hard truth is that all the rest of the SATA drives out there are your basic EIDE drive with what amounts to a SATA adapter built in, a PATA-to-SATA bridge chip. And so it is with my new hard drive. (source)
To ease their transition to Serial ATA, many manufacturers have produced drives which use controllers largely identical to those on their PATA drives and include a bridge chip on the logic board. Bridged drives have a SATA connector, may include either or both kinds of power connectors, and generally perform identically to native drives. They may, however, lack support for some SATA-specific features. As of 2004, all major hard drive manufacturers produce either bridged or native SATA drives. (source)
I also learned that my SATA II interface didn't at all mean I was going to get twice the theoretical 150MB/sec speed of an SATA drive. It actually doesn't mean much at all. It turns out the quality and speed of the drive itself, independant of the interface, and much more significant.
In spite of the manufacturer's true but hyped 150 MB/s claim, today's hard drive performance is based on the quality and design of the drive, not on it's being SATA or PATA. SATA (1.0) does support transfers of up to 150 MB/s. However, current drives and mainboards don't support those speeds. So don't expect a performance boost from your new SATA drive unless it is something like WD's Raptor. The Raptors get their performance boost (on par with SCSI drives) from being high performance drives, not from their inclusion of a PATA-to-SATA bridge.
(source)
Then came my own benchmarks. My UDMA/133 hard drive clocked in at ~49MB/sec reading from the disk (not the cache). My SATA II (again, 300MB/sec) hard drive hit ~56MB/sec in the same test. I'm now feeling pretty certain the difference can be accounted for simply because the SATA drive is a couple years newer, NOT because the interface offered any advantage.
I do recognize that SATA drives have some advantages. The biggest is probably the replacement of those damn ribbon cables and stupid crappy molex power connectors, for cable much smaller, easier to deal with, and able to span impressive lengths. Most SATA drives support NCQ (Native Command Queueing), and they also have other less useful (for most people) features such as hot-swapping capabilities.
However, until more manufactures begin making native SATA drives, and disk technology improves to the point where it can take advantage of SATA's available bandwidth (or we see something like solid-state memory hard drives with 300MB/sec or 600MB/sec [future spec] SATA interfaces) the "speed and performance benefits of SATA" amount to nothing more than a bunch of hype. If you want a good hard drive, buy a WD Raptor or a Seagate Cheetah or something. Whether it is SATA or something else matters much less than the rotational speed and general performance specs of the drive itself.
