I have no opposition to Di, I just don't think its really any great innovation. The limitations of any derailleur system is the fact that the chain has to be pushed to another cog or chainring. The limiting factor on speed of shifts is the cadence you are pedalling at and the torque you are exerting at the time you shift. Di still has that limitation. Mechanical systems are extremely precise, fast and reliable, I don't see Di as improving on anything major.