I've had a Di2 6870 Tarmac for the last 18mo and don't think I'll ever go back to mechanical. Ease of trimming the derailleurs wouldn't be part of the reasoning though.
I took the first ride on my newly electrified Diverge today. I would have liked to route the front wires internally, but already had a spare Junction A and with all the extra cables I'd need (and real handlebars rather than risking drilling holes), decided I'd wait for complete internal routing (or wireless) on some future complete bike. I do wish there were better options for seat tube battery mounting ... I ended up wrapping it in foam as I've seen everyone else do and shove it in (I'm using a seatpost I couldn't mount the battery in).