* Tubes giving away far too much. Whole movies are on those things. They forgot the golden rule of "tease"
* Actually, everyone forgetting the golden rule of "tease" with their free content.
* Search engines giving all the top spots to tubes, as KlenTelaris says
* A lot of content that isn't particularly original or different.
* Failing US economy
That said, I think there are still sales to be made. I'm going on the idea that if bottled water can become a billion dollar industry when you can just get it out of the tap, then I can sell my good quality porn even when the tube sites are overflowing.
