Save the Date Announcements are recommended for:
Summer Weddings Destination Weddings Weekend Weddings Weddings with many traveling guests Weddings near a major holiday Weddings which include guests with busy lifestyles

Save the Date wording can be very casual but should also give some indication of the flavor of your wedding style.

Some examples:

Please Save the Date
for the wedding of
Jon Stone and Tina Williams
27 June 2009
Santa Fe, New Mexico
Formal invitation to follow

You can add meaningful or playful text, if you like (and if you have room). A quote, a couplet from a poem.

You'd better remember
the 12th of September
James + Sandy will tie the knot
on the beach at sunset
Santa Barbara, California

If you are going to use a booklet style for a destination wedding, you can add recommendations for hotels, and a brief itinerary of the events you have planned for the weekend.