I found this older post where the reality wasn't very plausible
http://forum.gravityhelp.com/topic/blackout-dates
However, the question is nearly a year old and a lot has changed with Gravity Forms over the past year. Has anything been done to allow selected dates in the calendar?
Nope. Nothing has changed there. We've been working on adding the most requested features and enhancements first and will eventually get around to adding some additional options to the datepicker field in the UI.
That said, you can still customize the jQuery datepicker to exclude weekends, show ranges, etc. by manually adding some script to your theme/page template.
The datepicker component is straight from the jQuery UI library so you can refer to their documentation for how-to's.
http://docs.jquery.com/UI/Datepicker
Also, here's a link to another thread that discussed something similar.
