I bought a Crucial M4 256 GB SSD and tried to put it with a caddy in the place of the optical drive, running the OS. it recognized the SSD but couldn't boot from it. After a lot of tries, I solved it by installing the SSD on the main HD slot and putting the old HD on the optical drive space by using this caddy. Now, i've read that it's a good caddy, but i'm suspecting that maybe this was the cause of the problem, that it works ok on the HD but not good on the SSD. Just a heads up to anyone who has similar problems.