We're surprising our three and six year olds with a trip in a week an a half. We really wanted to surprise them, only partly because they would drive us nuts if they knew ahead of time.

However, we didn't think they'd really "get" the surprise, since they've never been to Disney World and don't know much about it. So, we started watching more Disney movies, and making casual comments like "Oh, I hear you can have breakfast with Stitch at Disney World", or "You can actually visit Cinderella's castle at Disney World." Those comments lead to more questions from the kids, and then we end up watching YouTube videos, and talking about what we'd like to do "if" we can go to Disney World "someday."
This strategy has worked pretty well, in that the kids definitely want to go to Disney World now, and they have a pretty good idea of what's there and what they'd like to do. But, they don't think we're going any time in the near future. Any time they ask to go, we tell them "Hopefully someday, maybe in a couple of years." I can't wait to see their faces next week when we pick them up early from school to go to the airport!
Clearly I'm a fan of surprising kids, but it definitely depends on the individual child's personality.