Hi,
Are you getting other system emails? Check your user_notify_admin.eml template and have a look for anything odd. Finally, turn on debug and try a signup and check the error logs for any errors about sending mail.
If it still doesn't work, and if you have SSH access, open up a support ticket with us with the access info and steps to reproduce and I'll get someone to take a look.
Cheers,
Alex
--
Gossamer Threads Inc.