From a traffic standpoint, it's not the day of the week, but the time of day. If I leave work just a tad early, I encounter the clueless parents que'd up in line to pick up their kiddies from school. It's just so amazing how their driving skills go right out the window during that time. You'd think they'd learn by observing each other ("My gosh, am I just as bad as the person in front of me?!") but I guess I'm too optimistic. Because of this, I'm usually not too anxious to leave work early.
From a physiological standpoint, Mondays are a hard ride cuz I usually do a long mountain bike ride on the weekend. I can still feel the fatigue in my legs on Mondays. But I'll take that over clueless drivers any day!