What, twice as fast as when you charge it with an iPhone wall adaptor??
Yeah, it's been we'll documented on MR that it charges the iPhone faster than the iPhone's native charger. I've never researched it to verify, but it sure seems much faster to me.
Interesting... I wonder if it's hard on the battery? Because if it were fine to charge it as fast as it charges with a 10W then Apple would have used a 10W adaptor for the iPhone too, wouldn't they?