My wife's '09 MacBook Pro (2.53GHz) was beyond slow and was irritating her beyond belief. I ended up bumping the RAM to see if that helped, but not a whole lot. Her issue was the stock 250GB HDD, which was slow as dirt. She had about 75% of it taken up, but it just lagged in retrieval speed. Time to move from HDD to Hybrid......SSD was a bit much in price for her overall amount of storage. Maybe next time :p
Installing the new 1TB Hybrid drive and new RAM (doubled and maxed her MB to 8GB) was very easy (just make sure you match the BUS speed.....I got 2x 4GB PC3-12800 for a little less $$$ than the recommended PC3-8500, but found out the BUS maxes as 8500). The instructions on this site were easy to follow and clear.
I had to download a cloning software (i.e. SuperDuper), so other than that it went smoothly. Cloning was super easy and straight forward.