Just completed the sign-up, but still get "We don't recognize that username. This is probably because you haven't been invited to our alpha yet. To request an invitation, please email join@app.net." when I try logging in.
xwowsersx, please send an email to join@app.net and we'll get you set up with your login information. The backing process and the alpha.app.net access are not automated yet, we still need to grant your user access to the alpha.