Everyone is talking about tube sites
 

So would it be smart to start building a few of them?

Fake ones? Real ones?

I'm surprised we don't see more designers using "I design tubes" in their own self-marketing.

bandwagons are usual.. i'm more interested in seeing the direction tubes take

Tube sites arent going anywhere. I would suggest using them just as you would any other traffic tool. There are plenty of great scripts that allow you to load your tube site with sponsor videos and display advertising along with your sponsor videos.