Do you have to send anything before an invitation?

Some people send a "save the date" card before the formal invitation. I am getting married in August so right in the middle of when people go on holiday. When we booked it last September, we put a save the date notification as a facebook invite and sent some save the date cards out so that people who are close to us didn't book their family holiday to clash with the wedding - we sent them out in October. Then we sent the actual invites with all the venue information and times and accomodation details at the end of February - this timing has been ideal for us in terms of getting things organized and if we had not told anyone until end of February we might have had people who couldn't come as they were away on holiday - this hasn't happened and almost all of our invited guests are able to come.

I think the etiquette is that you only send save the dates to people who are going to be invited to the whole thing - you'd be pissed off if you missed a holiday or you booked a day off work and you only ended up with an evening invite!