It's kind of a pain in the butt.  But you have to log on to your Ustream account.  
And then if you leave the page or look at post, you will need to log in again.   I'm hoping we can get around that, but it may be hard.  
It works slick if you want to get into a back and forth conversation without PMing like crazy.

One other way around it is to open up 2 browser windows, that way you leave the chat up while you surf. 

Sometimes I forget this is a new feature.   I just got done checking my email 5 times in the same thread when I could have just chatted to you all in the chat box.

The only thing I really can't stand about the chat box is the whole log in factor every time if you leave the page.   It's good if you're just hanging and talking.   

Anyway,  it's there.