I tried Di2 a couple of summers back at the NYC 5 boro tour. Granted, I tried it once in a parking lot...but my impression was luke-warm. I like the mechanical feel and trustworthiness of a good, purely mechanical group. I can see advantages for cross or MTB, but for my tastes mechanical is just fine on the road. The fly by wire feel of the shifts just ain't my cup of tea. I would still love to take a bike like the C'dale above for a good long spin with some climbs to really give Di2 a go.
I can certainly see advantages it holds for others.