Do you remember the Frugal Gourmet Show on PBS? Jeff Smith used to always swear by weighing flour. My experience is the amount of flour seems to vary in the same recipe for bread on any given day. Maybe the humidity plays part, and maybe the Frug's weighing accounts for that and I'm just not a believer. I find I have to adjust recipes by up to a 1/2 cup flour to get the bread dough kneading right.

Yes I have seen that Greg - and many bakers will NOT measure - only weigh. Humidity and temperature does play a very important role in baking and working with flours and even yeast. That is why you will see in many recipes (bread or sweet breads for instance) will say add as much of the remaining flour to get a smooth dough. Always go by feel, look, touch!