I have a SRAM Force/Rival mix on my Giant Defy purchased in Feb this year and so far on about 1500km including some 100-200k rides. I had the mix because the Rival crankset can have a Quark power meter but on Force or Red you have to have a more expensive spider based power meter which would make replacing the chain ring very expensive. Everything else is Force. The LBS made it easy for me to decide on this mix by offering a better price overall than for a Rival equipped bike - I think they had the components lying around and sales were slow that week.
My experience is that electronic shifting is very nice. A bit like getting an automatic car; at first you worry that it is more complicated, more likely to go wrong and you feel a loss of control. After a while you realise it is actually more durable, doesn't go wrong and is very controllable. The only problem I Have is switching back to my other bikes on mechanical group sets ad remembering how to change gear. My dyslexia doesn't help either.
My battery on the rear derailleur ran out on a ride recently. I hadn't charged it since buying the bike so it was my fault. I switched batteries with the front derailleur which I kept in the small ring and got around the ride fine. It was a hilly ride though so the small cog was fine most of the time. I could have left it in the big ring or just stopped and moved the battery around to change the front but that would have been a bit of faffing. I could carry a spare battery as well but they are 50 quid!
The need to push the left and right button at the same time to shift the front derailleur is sometime cited as a problem as you need both hands on the bike. I have never had a problem with having both hands on the bar at the points where a shift is needed so it hasn't ben an issue.
All the reading and research I did plus talking to friends suggests that long term e-gears are reliable and fixable. But in the unlikely event they do go wrong a long way from home the multi tool and puncture repair kit I carry are not going to be any help. It would need a LBS.
I do really like the Giant Defy. I like my titanium Enigma too. The Defy tends to stay indoors when the weather is crappy or the roads are poor when the tougher Enigma excels. The Defy is faster and maybe a bit smoother, quicker to turn, very reactive.
