I watched it again recently because someone I knew had never seen it. It's actually not very funny anymore. I am still amused at a lot of the jokes in it, but more in an academic sense because I remember how funny it was. There's a lot of stuff in it that's really funny on paper but just doesn't make you actually laugh anymore. Comedy doesn't really age that well, and I believe that it's because what surprises us and what's considered "clever" inevitably changes over time.
There's certainly something to novelty wearing off with time but I don't think that diminishes historical work. When I listen to Abbott and Costello perform "Who's on First?" (c. 1938) - it's still funny. It's not intrinsically less funny because I've heard it and things it inspired many times over.
It's also in how you watch things. I sometimes catch old films in the theatre and the room is filled with laughter. I was belly laughing to The Palm Beach Story (Sturges, 1942). Heck, I've been to see Shakespeare where everyone's laughing.
It wasn't funny when it came out, for me, and I was a big fan at the time :P
Steve Martin's comedy in general isn't funny anymore for me. I listened to his 70s albums which I found hilarious when I was a kid. Nothing about them is funny anymore. The jokes themselves aren't funny. It's only the delivery that made them funny and that style of delivery doesn't work anymore. He's been in some great movies, some of which are comedies and still funny but his own stand up comedy isn't anymore, at least for me.
