Circles is awesome. I can't believe Facebook hasn't done it yet. Hopefully you can drop friends into more than one circle.

As far as Huddle goes, I hope it's easy to go from a normal text straight into a Huddle. Also, typing status is very helpful in a chat room to avoid the inevitable conflicts that occur when people happen to type responses at the same time.

Sparks looks somewhat like Google News filtering. I'm not sure if I'll use it if that's all it ends up being.

Hangouts could be interesting, but because it's many-many communication like Huddle, the conversation flow could be difficult to maintain. I hope it works out.