I have a Mid 2009 Mac Book Pro. Had the same issue. So I upgraded ram from 4gb to 8gb. Didn't really help too much. This slowness really started when I upgraded to 10.8 MAC OS. Now I'm going to upgrade the HDD. I have a 320GB, which is partitioned, 220GB for Mac OS, and 100GB for Itunes. I'm either going to add a data doubler or just swap the HDD all together. I was also thinking about adding a small SSD data doubler 60GB, and use that only for the OS. Not sure what to do...
Mac Book Pro 13"in display
RAM 1066, DDR3 8GB