Originally Posted by Koyote

My sense is that most Di2 owners believe that it shifts better than mechanical...However, I find that a properly adjusted mechanical drivetrain shifts just as quickly and quietly as my Di2 bike. For me, Di2's most useful attribute is the consistency and reliability of the shifting -- it virtually never needs adjustment. It also offers a few neat tricks like Synchro and Semi-Synchro shifting (which I don't use) and a bluetooth connection that provides a gear combo readout on your computer.

Note that a full charge on a Di2 bike should get you at least 800-1000 miles -- probably longer if your bike is 1x. That should get you through most trips. Di2 is remarkably reliable, in part because there are no cables to fray and break. But as Rolla implies, a problem with Di2 may be harder to repair while in the field.

Finally, if you have to ask, then yes -- you will regret not getting it.