My iPhone 4 asks me to recalibrate the compass by using a figure 8 motion almost every time I use it.
I'm wondering if this happens because my phone is defective, or if other people are having the same issue.
According to an Apple support article:
After updating or restoring your device, you may notice that the recalibration alert appears more frequently. This is expected behavior, because the calibration database is being recreated. The frequency diminishes over time as you calibrate the device for various locations.