fuelmiser: yes, I get the hit every fall as well. My overall average is 4.84L/100 km (over 64,507 km). However, my winter time average (a spread sheet that I keep for all tank re-fills that are 5.0L/100 km or worse) is 5.46L/100 km. This is a hit of 13% from the overall average. My normal mid summer numbers are 4.56L/100 km.
I find that once the ambient temp (or wind chill of air entering the intake) is below 15C, one really notices the hit.
I employ a cold weather protocol from early October to mid April.
Said tips to save fuel in the winter with these cars can be found elsewhere in this chat room and here: http://www.cleanmpg.com/forums/showthread.php?t=17560