The iMac 1.83 Core Duo had a dead logic board.
Smoothly for the most part. I had to add a hard drive and move the heat sink from the dead logic board to the new one. Once I started installing OS X, my heart sank when there were no volumes available until I realized you have to partition the disk first. I was relieved that I wouldn't have to take things apart again.
Tape a note card to the work area and label areas for the screws that you take out, so you know where they go when you're putting things back together. Also take a picture before you start disconnecting things, so you know where the cables go. I didn't and got lucky that everything went back where it should, but the picture would have been handy to make sure.