My wedding is January 12, 2013 in Cancun Mexico. I sent my save the dates out 1 year, the day my fi's mom gave me her list, in advance to allow enough time for people to save money. They included the date, the resort location, and the website.
On the website i included estimated prices, that state they will be finalized in the near future. The website also has the RSVP and commonly asked questions.
I had my STD and lists of my side completed and was just waiting on a final list. Most guests appreciate the early notice (even without a date) so they can start saving money if they want to come!