Hi there - I have a similar issue to here - http://www.gravityhelp.com/forums/topic/gravity-form-not-working-for-everyone#post-79507
A client has not had a form submission since 22 February 2013 - usually they receive about 20 a day. On investigation testing showed that form submissions were a) not being sent to the email address set in the form notification field and b) the form submissions were not being added to the 'entries' list like normal. The last one was 22 February. I've turned off all plugins to no avail. When I do a test submission it appears to go through fine and the "thankyou" screen appears BUT there is NO record anywhere of the submission itself.
HELP!