I've read a few of the small prints, many offer a free 3 day trial but you need to pass over your CC details. They then automatically subscribe you to a monthly payment of 'X' amount unless you cancel before the end of the 3rd day. However I can imagine many people have had problems with this, all they need to say is they didn't recieve your email and I'm not sure how it works with different time zones.
All seems a bit dodgy to me- unless you intend to pay monthly for porn I would keep away. There is plenty of quality free porn out there and I'm sure you'll find a whole wad just looking through the 'video' section here at Freeones!