We had an old iPhone 3G that my daughter is using as a Touch. The battery got to the point that we were getting 30-45 minutes of juice after 24 hours of charging.
The process took about 45 minutes (slightly longer than the 15 minutes suggested in the video) but my time would definitely be less if/when I had to do it again.
The drama was that I didn't know if I got it "right" until I had replaced the battery, reassembled the device, and then let it sit to charge for hours. The suspense was killing me!
The process was really straightforward.
One thing that might have saved me a minute or two would have been to realize that there was a "Previous Page" link at the top of each page of instructions.
Basically, the walk through of the instructions have "Previous" and "Back" buttons at the bottom of the page, which makes sense since after walking through the steps you end up at the bottom of the page.
The "gotcha" is when you are reassembling the device you basically go through the instructions backwards, which means you read from bottom to top and end up at the *top* of the page. I then scrolled all the way to the bottom to hit the "Previous" button. I was two-thirds of the way through reassembly when I noticed the "Previous" button in the menu bar at the top of the page! Whoops!