I got my iPhone 4 on release day, and being as long ago as that was, it was time for a new battery.
The repair was as easy as watching MJ (without getting distracted by her charm) and doing what she did. About 10 minutes worth of work, and my iPhone lasts all day again. Yay!
As MJ says in the video, they really did put too much adhesive under the batteries on some of these phones, mine included. I highly recommend wedging the plastic opening tool in there gently to separate about half of the adhesive, then using the pull-tab to get it out.