I Was running out of space on my original HDD and wanted a little more snap regarding data retrieval. The reason I replaced the fan is the sound that it was making was unbearable any longer. Once I was asked by a family member - What is that crunching sound when my fan kicked on, that was it.
The repair was simple. As long as you go slow and pay attention - AND KEEP ALL YOUR SCREWS in plastic containers or magnetic bowls, you will have no issues. I also cleaned the entire interior of my MBP with lint free swabs - they get pretty dusty even when they aren't opened for 4+ years.
If you only have the original restore disks (mine came with Leopard) and you don't want to restore from a Time Machine backup. Make sure you have a DVD copy of Snow Leopard, Lion and Mountain Lion if you want to upgrade all of the way. I had a miserable time finding a copy of Snow Leopard online - Apple.com has never heard of Snow Leopard apparently BTW. That was the only part of the process that was any hassle. GOOD LUCK!