I have one in my GT and I wouldn't be without it.
Absolute doddle to fit, and a great idea. Only tool you'll need is the bent wire tool to remove the head unit (and you could get away without that if you really wanted..)
The Headunit can't do ID tags. This is the only disappointment for me.
Apart from that, good advice from the gents above.
I drilled a hole in the side of the glovebox big enough to fit the connector through (Dension Icelink Plus for me rather than Alfa OE version). One word of warning though - Pull the headunit out of it's slot first so you can get some light in the back of the dash and move any wires out of the way of the drill bit when it comes through!!!
Keeping the iPod in the dash with no external mounting or drawer to advertise it's presence is the best idea but the small downside is that you won't see the Alfa logo on the iPod screeen!
With the Dension system, the iPod controls are disabled when it is plugged in to prevent use while on the go, so there is not much point having it mounted on the dash. I've just given away my mounting bracket.