I'm always amazed when I meet people who have never seen a Broadway musical or can't hum along to popular show tunes. I was lucky enough to grow up seeing these shows at the big theaters on Hennepin Avenue, and dorky enough to rent the movie versions from the library. I was also a theater geek in school.
Not everyone has that kind of background, but with the Internet there is no excuse to not know at least one song from some of the major musicals. Once you familiarize yourself with some of these songs, save up your cash (or hop in the student rush ticket line for $20) and go see a show! Your life will never be the same.