We already have a thread about pornhub.com:
pornhub.com - Record XXX videos from flash player (http:// .flv)

pornhub.com offers HTTP .FLV streaming videos, and there are lots of ways to download HTTP .FLV videos.

One method of downloading videos from pornhub.com is called "View source method". You just view the HTML source of a web-page using your browser and find say .FLV in the text. Then just copy the URL and download it with your browser or any download manager. I don't even mention this method in the FAQ, because in many cases you can't find a stream URL with it, but you can always use URL Finders like freeware URL Snooper to find most stream URLs.