I used the invite code from Aviate as found on Aviate's facebook page. I'd post the link, but XDA it's blocked to prevent spamming.
the link looks something like this ==> uu uu uu.facebook.com/aviateapp/posts/195912073936304.
To save you the hassle, the code is "YAHOO". Apparently Aviate is giving out 15,000 invites. I used the code at 12:30 PM EST and it's been up for about 19hrs. There are only 84 likes on the post if that's any indication of activity.