I replaced 750GB HDD by 250G SSD (Samsung 840Evo) in Macbook 2012, i7 2.9GHz (Mountain Lion OS X). It runs very slow, and SBBOD appears too much. I was seeking support at apple discussion forum, but I got no solution except some opinions and "That looks like a problem with the SSD. If you hacked the system to enable TRIM, you're on your own." You may check my threads here and here Please share if you are having similar problem, or if you have found a fix for this problem.