I found this article interesting. We might have a lighting fast PC only to have the hard drive jumper in the default position and be running on half speed.
SATA-150 has a maximum data rate of 150 megabytes per second, not surprisingly SATA-300 has a 300 Mb/s data rate. Precious few hard drives can come close to a sustained 150 Mb/s transfer rate off of the disc platters and NONE can do 300. If the data is small enough to reside on the cache of a hard drive then the 150/300 jumper will make a ever-so-slight difference. The top tier of Solid State Disc Drives (SSD) can certainly hit close to 300 though.
Bottom line: If you're copying/reading a large file off a hard drive it isn't going to matter whether the jumper is set at 150 or 300. It will make a big difference on an SSD.
The Samsung drives I have don't even have that link. The documentation that comes with the drive does mention the possible problem of the drive not working with some of the older controllers in which case you need to download a "software switch".
The Barracuda 1.5TB drives I got a while back have the jumper, but it is not on AND if you do some research you discover that depending on the exact model, it may or may not actually have any affect on the drive (I was working with it a while back when it seemed the new drives were crashing my machine - turned out it was a failing power supply).
the only thing I have seen drive's be the bottle neck with is AVI, normal compressed formats drive speed hasn't been an issue for me, not even close. It's always the CPU.