Just found some great software called Dopplr. It's for frequent travellers and intended as a social network but also to enable you to find where your friends are travelling when so you can actually meet them on the way.
I once spotted ViolainVilnius on the front row of a concert in Kiev when neither of us knew we were working in Kiev. Ever since then I have been wishing there was someway to keep in touch. Some people tell you on Skype or Facebook, but that's usually too late for planning journeys to meet in airports.
Anyway Dopplr looks like it might do the trick. At the moment it's in beta and you need an invite to get to use it. But now I'm subscribed I can hand out any number of invites to my friends. Not much to see on the website until you get an invite.
Send me an email if you want to try it.