If I were to start a Ustream of some public games...

Would anybody watch?

It'd depend when it is running. But I love to watch the Youtube videos so yeah.

Yuck! Ustream is horrible for gaming. Justin.tv is the way to go if you want to broadcast gaming or anything in general.

Also it depends how your setup is. If you just have the stream playing what you watch that can get boring really fast. Interaction with your viewers is key when broadcasting games.

If you want to get an idea you can check the archives of these streams:
http://justin.tv/swiftor
http://justin.tv/hotbloodedgaming
http://justin.tv/rsqviper
http://justin.tv/chingy1337

I would if I am on the opposing team of yours during those games.