I always let one person know how I can be reached (these days, email, but if I am not going to have connectivity, a place / phone number) just in case of dire emergency (and they are good, at this company I have never been called while overseas).
I may mention that I will be away to others, to give them a heads up if we are working together on something etc. If they ask I will tell them briefly. I have no issues with people knowing I am going anywhere in the world!
When I come back, people often ask where I have been (especially if you have a tell tale tan etc) yesterday someone I know a little asked, and we got into a really interesting discussion on Mexico, she was under the impression it was a very unsafe place. I like to think open conversation helps people have a better understanding of the world.
I have also clued in some work colleagues to great deals etc. that I have found on here and round about, and it makes for a pleasant workplace when you can have some small talk about sunnier climes!