Quote from Daal:
This article says things alone the lines that I'm saying. The biggest bang for the buck comes from having an SSD with SATA 2, SATA 3 improvements are modest
4KB random writes are almost the same whether you use SATA 2 or 3 (except for OCZ, which is a POS brand anyway) and I believe this is the biggest factor in performance in a day to day basis. Boot time also didn't materially change and the article author even said don't expect a jump there
There is a jump in compressed files read and write but I don't think that is a big deal for most people
There is also a nice jump in the large file processing but again, its not something that people use frequently
Someone with SATA 2 might be able to get these improvements plugging the SSD in the USB 3.0 anyway (at least part of the improvement)
This might not matter in the US but in Brazil SATA 3 brands are sold at a quite a premium and SATA 3 in laptops are pretty much inexistent