Every holiday we have been on we have met someone we know. It's become a standing joke with our friends/family and it's one of the first things they ask us when we get back!
The best ones:
2004 honeymoon, made friends with another couple on honeymoon. When chatting the male mentioned that his dad was in the Army (as we both were).
A few weeks after we returned DH went to Iraq. About 6 weeks in, at a routine checkpoint DH sees a bloke that looks familiar, checks his nametag - it's the dad.
2012 on hols in Egypt, DD makes friends with a girl her age, we like the parents and we end up spending most of the holiday together.
2013 we go back to the same place. Start of week 2 I'm on a sunbed early morning and I hear "Eve, is that you?" They'd also decided to return, just a week later.
2014 Gatwick airport boarding for a flight to Kos I hear "I don't bloody believe it" and it's them again!
No contact with them after each holiday, just a great coincidence 
Last year in Egypt again, browsing FB one morning and a friend posts a photo from her holiday. I think, "I recognise that", and it turns out she's in a hotel down the road. I hadn't met up with her for a number of years (military friend) so we took the opportunity to get together.
This year on hols DH starts chatting to a family by the pool. Mentions the story about meeting my friend last year...bloke says, "I know a couple with those names" turns out he is the cousin of my friends husband 
I'll be quite sad when we break this cycle...