Yeah, they just sent me an email implying my hotel reservation wouldn't be complete if I didn't verify my email, but what they meant was my booking.com account wouldn't be complete until I did that. I've never used it before this but it was definitely unpleasant. Then again, I don't think that business revolves around delightful UX.

The only time I've ever used it they double booked our hotel. They put us in a place that was 3 times more expensive (at no additional cost) but the location was really poor.