I love Gravity Forms, and I've used it on a dozen sites so I was quite surprised when I installed it on my personal blog and couldn't get it to save the form. It was coming up and saying it saved, but when I clicked "Continue Editing This Form" it would bring me to the new form creation screen. No matter what I tried, nothing was getting saved.
Being a PHP developer, I decided to do some debugging. I opened up Firebug and started looking at the AJAX requests. To my surprise, the requests were being sent to save and getting a valid response. Looking at the response I was getting "EndInsertForm(0);". I did a quick grep and discovered that the 0 was supposed to be the ID of the newly created form.
it obviously was having some sort of issue, so after a bit of debugging I realized the database tables hadn't been created! It turns out my DB user didn't have the permission to create tables (For some weird reason).
Anyways, I think Gravity Forms should display some sort of notification saying that it was unable to create it's tables and will not be able to function. This may be sort of a fringe case, but it is easy to implement and might save some headaches.