I ran friction shifters on my TT bike for years...the long cable runs and tight bends created a fair bit of slack and cable stretch and it was nice to always find center.

With Di2 it's a perfect shift, every time. Stuff's amazing. Front derailleur trims itself. At one point I was lugging up a hill and an electronic voice asked me if I would like to downshift.

OK, not quite, but it's really nice stuff.