I installed it myself, on a scale of 1 to 10, maybe a 5, the biggest problems were:
a) to route the iPod cable to the center cubby as you have to take the center console out
b) to get the head unit back in the hole with tons of cables hanging from the back
c) to do a nice job with the dremel tool
d) placement of the GPS and XM antennas
Here is a list of links I used to get the job done:
http://www.renntech.org/forums/index.php?showtopic=19074&hl=double%20din
DIY Instructions - Avic D3 Installation
Best place for GPS antena
http://www.renntech.org/forums/index.php?showtopic=20442&st=0&p=105137&#entry105137
http://www.6speedonline.com/forums/996/84794-finished-kenwood-dvd-nav-install-ac-control-mod-pics-some-diy-stuff.html
by the way the guy who posted the first thread (trieullionaire) is also the guy who sells the mounting harness on eBay, I HIGHLY recommend to get the harness
w/o the harness it would have been a 9 or 10