iTunes Skip Algorithm

I use the Last Skipped date in several Smart Playlists in iTunes. However, a lot of songs that I think I skipped don't show up as having been skipped. I just skipped a bunch in iTunes and found that if you push next before 2 seconds have elapsed the track will not realize it has been skipped. I assume this is a feature in Apple's eye, and I don't really mind it... but I'd like to know the full algorithm. It appears there is also a boundary on the other end... if you let too much play it doesn't count as having been skipped.

Anyone know?