I kept this computer because it had the wonderful 17" monitor that I loved for watching movies. But the once mighty 200 GB hard drive was another story. I had gotten used to an external drive for the iTunes and movies directory but I discovered that the moment I used the computer without the external drive the iTunes directory moved itself back to the local drive. I'd move it back and try to remember not to do it again. Eventually this and other things got inconvenient but I assumed that replacing the drive was going to require an expensive professional intervention or my taking a chance with my own personal repair inexperience. I hesitated forever until one day the drive failed and I decided I had nothing to lose.
The repair went astonishingly well. Absolutely smoothly, exactly as the guide showed. I thought it was going to be like trying to do surgery on a cat, having seen the complex, tightly layered spaghetti/origami world of mac electronics in tear-down pictures. I had assumed it would be way to easy to twist, bend, tear, or break something in all of that. Instead it was easier than following a cooking recipe. It was mostly removing and replacing screws. Without the pictorial guide, though, and the correct tools I got through iFixit I wouldn't have had a chance on my own. I wouldn't have even known that there was something called a Torx screw, what size screws these were, or how to find any of that out. So really, the guide and the tools were 99% of what was needed. My job was the easy part.
I would suggest reading the notes and comments people add over time at the bottom of the guide. There can be small variations between the same model devices. There are also little details that some people ran into problems with that their comments help avoid, things you'd only know by already having bent something or pulled something the wrong way. Or even suggestions that allow you to leave a connector in during the repair rather than completely pulling it out and then having to figure out how to get it back in. I added a particular method that may or may not be needed: I have often found that screws, after many years in a particular location, are not as interchangeable as when things are first being assembled. So I carefully put the screws into rows that matched the images in the guide and taped them in that position so I could replace them in the exact location they came from.