Apple does a fantastic job with their hardware; for the exorbitant prices that we pay for these machines, they are definitely pretty beefy to begin with. However, it is also understandable that they try to balance power with endurance, so it is not surprising that they opted to put in a meager 5400-rpm hard drive to conserve battery life. The problem for me is that I am an atypical power user - I often run two or three web browsers, a huge Java-based IDE, VirtualBox running Windows, Outlook, and whatever else that I may need from time to time - all of the time. This gets to be pretty expensive when it comes to disk reads and writes, and the poor little 5400 just couldn't keep up anymore.
iFixit did a bang up job with their upgrade kit. Not only did they include the hard drive of my dreams, but they also threw in a screwdriver set that will work for the MBP screws (and then some!), and an awesome little external drive enclosure so that you can continue to use your OEM hard drive even after you finish copying over all of the data (can we say secondary backup drive?). The process itself is almost as simple as upgrading your memory: you remove the back cover, unscrew a few screws, plug in the new drive, and put everything back again. I had more difficult taking my Xbox apart.
If you use FileVault to encrypt your hard drive then I would strongly recommend that you decrypt your drive first and then renecrypt your drive after you've copied all of the files back. When you format your drive with encryption using DiskUtility it is not compatible with whatever it is that FileVault does to your drive - I was not able to turn off FileVault. So I had to put my old drive back in, disable FileVault, and do the whole copy process over again.