1) I have a theory that you can identify a pop song by the fact that once one learns/understands the words he will almost immediately become bored of it. This explains why many pop songs (like Beyonce's) are so good for awhile but then suddenly become unlistenable, why so many succesful rock bands have lead singers with whiny voices, and the amazing staying power of Shaggy's "It Wasn't Me" (because you can't understand what he's saying). Musicians face a trade-off in that you want the listener to understand enough to get the general idea but you cannot allow the listener to understand everything.
2) Songs are substantially more likely to get stuck in your head when the most recent time you listened to it you didn't listen to it all the way through. I think the reason for this is because unconsciously you try to "complete" the song and that some of that attempt leaks into consciousness.
3) It is a commonly used tactic to listen to music for pump up purposes. What is underused is anticipating that you will need to be pumped up later in the day (to play a big game, study, etc.), and listening to highly chill music in the early stages in order to avoid ego depletion. You should then crescendo the intensity of your song choices slowly until you are listening to the best pump up material right before the big event. Pump up music is relative so the contrast will help produce a greater effect.