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
CPU 2.53
RAM 1066, DDR3 8GB
HDD 320GB
Video 256MB