I test rode Ultegra di2 for 30-40 minutes at a Trek demo event. I noticed the same thing about lack of tactile feedback. Those buttons feel more like micro switches. I couldn't hear the RD when I was moving so I wasn't always sure it had shifted. Rear shifting wasn't any faster than mechanical IMO. The demo bike I rode was making clicking noises in certain gears too. I'm not writing off electronic but I wasn't impressed enough to start saving up $1500 for it with the seat post battery.