Not the candy/holiday tradition, of course, but the trivia fodder sprinkled throughout entertainment media. I would say 'modern entertainment media', but the practice of making references is basically a form of mild humor, and for that reason I'd bet it's as old as time.
Anyway, when I actually find them, I react to them probably as anyone would: with mild delight.
Unfortunately, due to the influence of certain people, I'm starting to get annoyed by them on principle. They're conflated in my mind with dozens of repeated viewings of shows I used to love, to the point where I can hardly stand them anymore; as well as being told all the reasons why I 'have' to go back and watch something I have no interest in so I can catch the easter eggs I missed in something I actually did watch (and enjoyed, until they saw fit to point out that I somehow wasn't enjoying it enough).
They've become symbolic of that fandom subculture that has 'rules' for being a fan, and insists that if you only like something casually you don't really like it at all.
And it really sucks, because I know that isn't how it's supposed to be. Easter eggs are fun to make and more fun to catch, when you're not bogged down by that kind of thinking. And if you make a point of actually hunting for them, it's just supposed to be an enjoyable challenge, like getting 100% completion on a video game. It's a great achievement, but if you emphasize it to the point where it destroys your or others' enjoyment of the game, what do you really gain from it?