For anyone that's having trouble with the jQuery UI Datepicker, pay extra attention to the version of jQuery UI and the API methods you're using.
For whatever reason, Gravity Forms v1.6.9 is [as of this writing] using an extremely outdated version of jQuery UI -- they're using a legacy v1.6 (April 2009), when the current release is v1.9 (October 2012).
The reason this matters is that the Datepicker has undergone significant changes on how it expects date values.
For example, to set the minDate/maxDate using jQuery UI 1.6, you need to use:
$('#input_2_15').datepicker('destroy');
$('#input_2_15').datepicker({
// Date(yyyy, mm - 1, dd)
minDate: new Date(2012, 10 - 1, 25),
maxDate: new Date(2012, 10 - 1, 30)
});
In newer versions of jQuery UI, you can use the more common mm/dd/yyyy format:
$('#input_2_15').datepicker('destroy');
$('#input_2_15').datepicker({
minDate: '10/25/2012',
maxDate: '10/30/2012'
});
I wasted nearly an entire day debugging this problem.
If anyone of the Gravity Forms developers are listening, please upgrade your JavaScript libraries, or create a filter to allow us to choose which version we want to use!