5 - 30 minutes
My MBP is 5 years old now and the 200GB drive that came with it just wasn't big enough anymore. The 750GB 7200RPM drive upgrade kit was jsut what I needed to extend the life of my machine. I also boosted the memory from 4GB to 6GB.
Very well. I printed the guide and used it to store the various screws by each step as I went along. Everything went smooth. I had backed up my machine with Time Machine to our Time Capsule and the restore went without a hitch. I have not over 500GB of free space where I was struggling to keep 20-30GB of space before.
If you are worried about doing surgery like this on your machine then review the guide and go for it! I was and it went great. The guide is clear and the tools that iFixit provides with the kit are just what you need to get the job done.