ViniferaMike wrote at 2012-12-29 19:04:34
According to Mississippi State University Extension, "There is no evidence that bleeding is harmful to the vine and is a normal process." MSU then goes on to explain that there may be certain benefits of bleeding.
Additionally, to counter Kathy's recommendation (Sorry Kathy!), it's better to wait until the colder weather of Jan and Feb to prune. This gives the grapevine plenty of time to store any nutrient reserves that may be left in its' shoots (they are stored in the roots).
My knowledge comes from two years experience growing grapevines on the East Coast and working with some of the best viticulture consultants around.