My wife and I saw this movie on cable TV shortly after it came out and shortly before it disappeared into oblivion, and since we both were little kids in the 70s we both found the movie to be pretty funny. It has its share of really bad jokes (like people slipping on a picture of bananas), but it's not supposed to be intellectual humor. It's supposed to be a campy, cheesy movie that (fondly) makes fun of a decade that contains a lot to make fun of. And it certainly succeeds on that level.
The movie was clearly a very low budget affair, yet the film makers managed to nail little details like the red, white and blue-painted fire hydrant outside the main character's home (there was one of those across the street from the house I grew up in). Everyone involved in the movie seems to have done their homework, but are having fun with it and not taking it too seriously.
I recently discovered that this movie has finally come out on DVD, and at a bargain basement price, so I ordered a copy. My 14 year old daughter watched it with me and loved it - she described it as "stupidly beautiful" and immediately put the soundtrack on her iPod.
So if you're feeling nostalgic for the 70s and think you'd like a low-budget comedy that doesn't pretend to be masterpiece theater, look no further. On the other hand, if 80 minutes of disco music, cameo roles and jokes about bongs and pop rocks doesn't sound like your cup of tea, then avoid.