One of the decisions we made before we left was to NOT talk about our trip on facebook or twitter until we were back at home. The deal is that it's not that hard to find out where we live and letting everyone know we'd be out of state for several days didn't sound like a great idea for the security of our house and possessions.
So we didn't talk about it online, and you know what? It was kind of hard. We belong to these communities because we like the people in them (generally speaking) and we've grown accustomed to sharing what we are doing (and getting feedback) in real time. Sure, we shared things when we got back, but by then, those things were yesterday's news, old and stale in our now real-time information flow.
The question I have is this: Do you twitter/facebook leading up to and while you're on vacation? Why or Why not?