How to Fight Lap Swimming Boredom

When I tell people what I do for exercise, I often get replies such as, "I would swim, but its so dull going back and forth ad nauseum." Well, I don't claim to have the secret to fighting lap swimming boredom, but I've done it long enough to agree it can get dull. Here are some of the things I do to keep up my enthusiasm.
1. Set goals (both mini and macro) - achievement makes it all worthwhile and pulls you back time and again
2. Use other swimmers like racing dogs to the rabbit at a dog track. Try to catch and pass them. Then do it again, and again. If they are too fast, just track your progress relative to them with markers in the bottom of the pool like the drain or lights. Note where you are when you pass the other swimmer even if they are going the other way, then when you get to the same spot the next lap, see if you have increased any distance between you and that swimmer (or have they gone faster than you?).
3. Watch other swimmers' swim style (under water). If they are better than you, try to determine what it is that makes them better then try it yourself.
4. Watch what is going on around you. Things are always changing and just noticing little things can get your mind off the repetition you are doing.
5. Wear a digital watch. During your turns, note your time. I often like to do mental math to calculate simple things like speed and laps to go in how long, etc.
6. Change up your stroke. I do freestyle primarily, so one might think I'm stuck, but I'm not - I change the sides I'm breathing on. I work one side for 400, the other side for 400, then change the breathing rhythm e.g., 5,3,change sides 5,3 ... 5, change sides 5, etc.
7. If none of this works ... Some people listen to tunes or even audio books using a sealed MP3 player with special ear buds that keep the water out.