Just picked up one of these myself. Time taken from beginning to end was about 90 minutes with the toughest part of the process being trying to re-align the hooks of the seat backs in my cabrio. Beyond that, everything was exceptionally simple once I confirmed that there was no "support structure" behind the side wall carpet in the trunk that I might ruin if I just yanked it out.
Disconnected the changer and plugged it into the iSimple. Ran the cable up to the front, tucking it into the molding along the way and feeding it up to the sunglasses/accessories cubbie. The only mod required was pulling out my Dremmel to make one of the holes in that holder a little longer to fit the connector through.
Easily the best $100 I've spent in a LONG time