I will add this to our recent PM exchange on this topic: while I like my DI2 system, I don't think it actually shifts any better (or faster, or more quietly) than a high-quality and well-maintained) mechanical system. I know plenty of people disagree -- and am interested in your opinion -- but that's been my experience.

I still do like the Di2, though. No cables to break or replace, no occasional tweaking of the indexing, and I love being able to glance at my computer and see my gear combo. Oh, and having fewer cables wrapped around the headtube is prettier, too.