I have just ordered my first SSD. It is a SamSung 470 64GB SATA II. It only cost me £41 witch is around $65 for you Americans. I had the option to get a SATA III for £47 but the SamSung came with Norton Ghost. I am only going to use it for installing Windows7/8 on. So would I have noticed much or if any difference between the 2?
SATA 3 SSDs generally perform almost twice as fast as SATA 2 SSDs, so yes, you would notice a difference as long as your motherboard supports SATA 3 and as long as the SSD takes full advantage of the extra bandwidth.
The difference is that Sata 2 has less bandwidth. If the SSD can max the SATA 2 limit of 3Gb/s then having a Sata 3 (6Gb/s) connection is a lot better. My SSD was slower on my old mobo and its much better.