I won an overseas trip a few years ago. The trip had to be taken during a 3-month period, and we were asked for our preferred dates and given the option of extending (at our own expense).
In the end, we didn't (no-one was willing to babysit our kids for longer than the initial timeframe!) but it was good to know the option was there. I've heard of other people also extending trips that they've won.
I've always wondered with these 'flights + x nights' competitions - are people able to change return dates easily? Flying 24hrs each way for a four night tour… I'd want to tack on another week or two (own expense, obviously) to make the trip truly worthwhile. So… any winners out there care to share?