Sponsor/Webmasters - what do you think about the "Tube" sites?

Do you think they it is beneficial to you, have some marginal benefits or just stealing your traffic?

For sponsors, if there are water marks on the pics / videos uploaded to the site there is a strong chance that surfer who likes the content might just type in the site name and go directly to your site. Does this happen?
On the other hand, since they are seeing a lot of free porn, surfers might just move on to the next video or photo set and not be tempted to look "outside".

Webmasters can upload downloadable content from a sponsor and post a referral link. However it is not very prominent, and nobody is going to even look at it, which obviously has no advantages to them while adding fresh content to the site

Just wondering where all of you pros feel about these "free porn" portals