Ajax Submitted forms with ENTER
I realize this is an old thread but it shows up high in the Google search results.

Just set your submit button's Ajax event to 'click'. I believe its default value is actually 'mousedown' which won't make it trigger when the enter key is pressed within a field of the form.

If you set it to 'click', that event will trigger when the submit button is clicked as well as when the enter button is pressed within a form field.