Signed up with my Gmail account and it appears your activation emails are going straight into spam on Gmail ... may want to look into that, or have someone who knows how to setup DKIM/SPF do it for you.
I know you guys are using Google Apps, but you should still setup the SPF and DKIM (checked default) records, which I don't see any under your domain (or returned from the DNS server).
Another option would be to use a service like SendGrid (their free tier supports like 12k emails a month IIRC)
Let me know if you have any questions or need help, i've had to do it for a large number of clients. Looking forward to participating and contributing on this site, thanks for setting it up!