Charles mentioned his own personal rule regarding working on Mondays no matter what. That got me thinking about all those years when I got up at 5:24 a.m. to go to work (yes, I'm spoiled; I no longer have to get up early for work-related reasons on any day other than Tuesday, and I actually get up earlier that day than is necessary in order to ensure that I have some personal time for reading, writing, etc., before I hit the road).
I never took Mondays off unless I was so incredibly ill that I had no choice. Likewise, I didn't take Fridays off. My rule was simple: Wednesday is the day to take off for personal reasons.
Two day work weeks are nice. If I took a Wednesday off, I had a Monday-Tuesday workweek, a day off, a Thursday-Friday workweek, and two days off. That seemed like the absolute best use of a personal day, and it made the week zoom by.
Now that I'm retired and only work two jobs (Comic Shop News and Dr. No's), I can't really take Wednesday off, since it's new comics day. It's also the most enjoyable day of the retailing week, though, so it's not a day I'd want to take off.