I think I'm pretty good at pegging what people like when it comes to the whole dessert / snack thing. Certainly I've become better at it over the years - I generally know how far "outside the box" I can go with my offerings before I start meeting resistance or (perish the thought!) outright rejection. It's all about picking up on the subtle cues people leave in conversation - even if you aren't talking to them about food (what, there's another topic of conversation out there?), people do drop hints as to their personality and generally their likes and dislikes.
A classic example I've come to realize over the years is that, for the most part, adults are perfectly content with desserts and snacks that are more spicy than sweet. They are the dark chocolate people, the ones who eat the actual gingerbread of the gingerbread houses (rather than people like me and most kids who would rather pick off the candy and royal icing), and those who lean towards fruit and nut types of concoctions rather than a sticky-sweet nougat or caramel.