I haven't heard that one much since school. People who are smart themselves and want to offer a compliment usually say something more specific ("you know alot about X"; or "I'm impressed how well you solved Y problem"). "Wow, you're smart" is usually spoken by people who aren't "smart" enough to respond more meaningfully to whatever was said or done, and often bespeaks a misplaced sense of awe, or even an attempt at empty flattery.
I like it much better when people are specific with their praise. I try to do the same for them, because it seems a lot less like BS then.
I think it disturbs me that my family considers me "the smart one" and I do also hear it a lot from other people...and I'm not even the smartest person I know, I know people who are much more intellectual, people who are in grad school, or who have pursued PhDs...I don't know if some people have ever even met a highly educated NT if they think that *I* am one of the smartest people they know.
Not to put myself down, but I see things on a sliding scale, and I consider myself intelligent, yet I don't understand why other people are so impressed with me sometimes. It is kind of depressing to think about what that says about society in general.
"Sentiment without action is the ruin of the soul." - Edward Abbey