You know you listened to a song too much when ... Even after having not heard it in several years, you recognize it immediately even after only hearing like 2 or 3 notes in the music (and only part of one vocal syllable).

Me a couple minutes ago, hearing Hoobastank - The Reason.  (Music at a local Baskin Robbins had been playing something else - I think Britney Spears - Oops, I Did It Again, then someone switched it mid-song to the other then immediately went to something else I didn't recognize.)

Reminds me of a time at a church gathering, we were having a contest to see how quickly we could recognize songs we knew, with someone playing them on piano.

Some of us were correctly guessing after hearing like only TWO NOTES!