I installed mine myself. Didnt take too long, but a little bit of cutting, drilling and it's in. I basically followed the install instructions for the BMW iPod interface (I bought one on ebay and it was a dud, unfortunately so tried the Kenwood instead). Follow here
http://www.e90post.com/forums/showthread.php?t=30079. You need to mount the box slightly higher behind the glove box to clear the wires. I pulled power from the homelink fuse in the fusebox. For now I have the LCD in the ash tray, but I am working on fabbing an inset mount where the center speaker is for some (I don't have obviously). Had to shape the controller mount just a bit to get it to fit on the console without bending it. It is definitely nice to have that control at your fingertips. For $50 from Crutchfield, well worth it!