This is a big win for Ustream. </captain-obvious>

And, relevantly to YCombinator, a big missed opportunity for Justin.tv :-/

I'm curious what differences there are between the services that would make Facebook pick Ustream over Justin.tv. Was it something in function? Aesthetic? (Ustream's front page admittedly looks a lot sexier.)

Ustream has a much stronger brand name than Justin.TV. One sounds like a youtube streaming site, the other sounds like one guy's TV show.

But Facebook doesn't care, because their brand overrides everything else. Name doesn't matter during a collaboration of this size.

Facebook definitely has more stature, but I'd say the opposite of your comment holds true. The larger companies are scrutinized more and have a higher standard of quality to uphold. Larger companies choose the best possible and the most professional partners. If things go wrong, the bigger company suffers more when it comes to "brand".

Maybe for everyone that enjoys using it as well. This will make so many people start using UStream that had never heard of it before. I'm not sure if they were in any danger of "going away" anytime soon, but certainly they aren't now.