I ran the original Dura Ace Di2 for over two years -- through all kinds of weather (including submerging the RD in flood water). I loved it. Nothing else compared.

But let me say that I did have one issue: Di2 is STRONG. It will shift under load, while climbing, no matter what. One time, a long, long time ago, I shifted under load while climbing out of the saddle on a 17% grade. The shift executed fine but the chain started making a repetitive noise. After I got home, I inspected the chain -- the Di2 shifter had bent one of the links of the chain in executing the shift. It happened once. And it wasn't a catastrophic failure.

I'm in the market for a bike now, and my next bike will have Di2. I won't consider anything else.