I have a form that has a dropdown which is tested for a yes/no answer. If yes, then the rest of the form displays including the Submit button. If no, then nothing but the dropdown shows up. It's setup this way for user registrations, only members of the organization are allowed to register and the dropdown acts as a filter for registrations.
The form stopped submitting with a recent update, not sure if it was WP 3.5 or a GF update. I tracked down the issue to the conditional logic set in the Form Settings > Advanced tab. If I have it set to hide the Submit button by default the form does not submit, either via AJAX or regular. However, if I turn the conditional logic off on the form and show the submit button by default the form submits just fine and registration works as expected.
Thought i'd share my findings here.
Bret