Just had my first geology hangout yesterday. I'm amazed it worked with my Linux desktop. Nothing ever works with Linux! I could use the g+ extras, and share my screen.
This is a brave new world, but it will be limited by those nasty time zones, and my old-man need for sleep! We had a grad student from Egypt, but students never sleep. :) Everybody will have to upgrade their equipment as well, since there can be a lot of static with bad mikes, etc.
For popular hangouts, the next phase is the lecture format, where the hangout is streamed to youtube. I don't think earthquakes and geology will ever get to more than 10 people, though. :)