For those in the market, there's also a dedicated channel ##atom-invitations. Make sure to also checkout discuss.atom.io. Note: the Atom beta is only available for OSX 10.8+
Once you get the invite, the first step is to authorize access to your Github account:
After that, you're free to download:
I can't wait to port my Solarized Darcula theme over!
Edit: port complete: