I have had a disproportionate share of close calls -- and one T-bone collision -- on Friday afternoons. I now try to remind myself on Fridays to be extra cautious and take it easy on my speed.
I think the difference on Fridays is people on their mobiles connecting with friends on weekend plans. I've also noticed a lack of turn signals particularly on Fridays, again perhaps because one hand is occupied with a phone or a beer.