While I was searching around trying to find the Lemond formula for saddle height I found this paper regarding the ability of different sizing methodologies to provide cyclists with the optimal knee angle of 25 to 35 degrees at the bottom of the pedal-stroke.

Comparing Methods for Setting Saddle Height in Trained Cyclists

Worth a read if you care about these sorts of things. Essentially they came to the conclusion that the best method is to use your heel such that when seated your heel just touches the pedal (at the bottom of the stroke) with your leg fully extended/straight. All the calculations based on inseam and such are far less accurate.

edit: google cache makes the link-maker thing freak out

interesting, i just checked both of my bikes and they fit this rule the way i have them set up.