I use GNU/Linux (Fedora) and do not use nonfree software. I'd be willing to use one piece of nonfree software for a purpose as awesome as this but I'd really rather try to find a free alternative that we can all use. I installed Adobe Flash (fucking bloated piece of shit that doesn't play too nice) last night just to see if Tokbox would work but it is waaaaaay too choppy (and reading this thread that isn't solely due to my old computer) to be worth using. The most promising application I find with a quick search right now is
Ekiga, although it does not appear to have a Mac version.
QuteCom has GNU/Linux, Mac, and Windows versions. The website is rather bare and I do not have time right now to investigate either of these further.
Pidgin has webcam support for XMPP (GTalk and Jabber) but Ionno if it supports conferencing or just one-on-one video chatting.
I think we should aim to do this at least once a week.