Heavy frost in late November '12!  Temps were in the mid 20's.  Blueberries really benefit from late Fall and Winter chill.  Any time below 45 degrees constitutes a 'chill hour' and it is an important factor in healthy blooming/fruitset in the Spring.

See how the frost accumulated more heavily on the western side (shade side) of the row.  It looks like snow it's so thick!

This closeup shows ice crystals on the bark mulch at least 1/4" long.  Amazing!