I think it would be a great addition for Gravity Forms to have the option of building a customised search form.
The builder would allow you to build a form with dropdowns / text field for post categories / custom post types etc which can then be used to search for particular types of posts or a general site search.
I can see it being used in many many ways and would be very useful.
Especially if you can allow multiple search boxes on a site as well. Then we can create a form for the general site search and then one for custom post types perhaps but with filtering.