The people that I know that do use booking.com, use it because they do not take any money up front, and most hotels are cancellable. Where as you have to pay up front for Expedia.

On the flip side, since they do not take payment up front, they FAX your credit card information to the hotel, along with mailing address, etc. Personally I would rather pay up front and have my info more secure.

15% commision is not a lot compared to what Expedia is paid. But then the exposure is not near as good either.

I really would not hesitate to use Booking.com if they had what I was looking for at the right price. But they normally dont offer me anything I cant find somewhere else easier.