The May issue of the San Francisco newspaper/magazine City Bike contains a two-page article describing the new 2011 Zero X and MX models, written by Charlie Rauseo, who says that he was a Dakar racer.
To make a long story short, he found the Zeros intriguing and fun to ride, but felt that they were not quite up to the performance of even an 80cc dirt bike. He said that some of the faster (and lighter) riders from Europe were able to run the batteries down in only 12 minutes of riding. At typical trail speeds the battery is good for 30 minutes. Changing the battery and installing a spare only takes a few minutes.
He liked the handling, but the brakes were only so-so. He says that he could tell little difference between the two models in the way they performed, although the MX uses a more powerful Agni motor, which is not used in the X. Mr Rauseo and other riders at the introduction did not care for the poor throttle response of the Zeros.
He felt that the rear shock could was fine, but Zero has an optional Fox shock that they sell for $675, which he says is better. He says that when he rode hard, the bikes would get hot, fans would come on, warning lights would blink and the bike would just stop until it cooled down.
After riding the Zero, he stopped by Scuderia West and test rode a Brammo Enertia. He found that the Enertia pulled a little better at lower speeds than the Zero, "but neither bike was impressive by any measure". He recommends that Zero dial in more off-the-line power as soon as they can and that both Zero and Brammo work on their bikes "throttle response", which I take to mean he wants more power off the line when the throttle is first turned.
Personally, I am not sure I agree with Mr. Rauseo, as I prefer a soft throttle response when moving at slow, parking lot, speeds. But then I am not a racer and use my motorcycles mostly for transportation.