I got this one from Uncle Jim Rowley at the 2005 Beemer Bash in Qunicy,CA. Jim says that you should fill your tires a few pounds above the recommended tire pressure. Here is a test to see if your tire pressure is correct.
1) Measure your tire pressure when the bike is cold.
2) Ride the bike for at least 10 minutes so the heat of the tire causes the air inside to expand and the tire pressure to increase.
3) Park the bike and test the tire pressure again.
You should see the tire pressure increase. The ideal increase is 6 pounds. If the increase is less than 6 pounds you have too much air in the tire. If the increase is more than 6 pounds then you need to put more air in the tire. If the increase is exactly 6 pounds, you are at the optimal tire pressure.
Thanks Uncle Jimmy!