As a regular and frequent online shopper I have noticed that quite a few sites switch off autocomplete on email fields.
For me this doesn't make too much sense, I am more likely to make a mistake typing my email than selecting it from an autocomplete list (indeed, many sites also just use one field for email without confirm, exacerbating this potential problem), not to mention it slows me down. While I have no evidence to back this hypothesis up I would be surprised if I was the only one who is like this.
What is the rationale behind the decision to do this during more critical online interactions like checking out or logging in ?