We're on Google Biz Apps, and we use Hangouts almost daily for team stand ups. It works really well, the audio is very good, and the collaboration tools are very good. We've been using screen share + Reflector to show off builds of our iOS product
I've also used it twice with an iOS device where I was offsite, but on a really stout LTE connection, also worked great.
We use Message (in OSX/iOS) for quick communications, but if we need to chat, we almost always turn to a Hangout (the audio is always better than a couple of our teams cellphones).
Ok, it's in the App Store now.
Q: how do I enable Hangouts for Google Apps?
As long as you have a Google+ account you should be good to go, and if I recall, our Biz Account had it automatically enabled as soon as I setup my G+ Our team (on the same Biz Account) was already a group that could be selected during a Hangout.