Is Friday the 13th unlucky? PubMed says yes. Dutch insurance statisticians say no.
On Thursday the 12th I used my debit card at Valhalla's to purchase the 4th Edition D&D Player's Handbook and In Your Face Again, a collection of Feng Shui scenarios. I then drove to Burrito Express and paid cash for a carne asada combo plate. I then drove around the corner home, got the mail, put my books, laptop, and bag on the counter, curled up in my hammock to read about new races and classes, and fell asleep with the radio still on.
On Friday the 13th I took Smoochie to the vet for an eye checkup. It looks real bad, but it could be a lot worse. When I attempted to pay, I discovered my debit card was not in my wallet. I promised to come back with a check, went home, and called Valhalla's, discovering that they don't open until noon. I went to work and called again. The phone answerer didn't see my card, but said I should call back later when another guy would be there. Before I left work I called again. This guy checked around the register and in the safe, but couldn't find anything. Rather worried, I drove back to Burrito Express in case the card had fallen out of my wallet. No such luck. I returned home and re-checked all three places I could have misplaced the card the previous night. Resigned to canceling the card on Saturday the 14th, I headed up I-70 to check the neighbors of Valhalla's and to lighten my heard with Friday Card Game Night at Witches Brew. Nobody had returned the card to the dojo/dance space next door to Valhalla's, so I checked back again. The third time was the charm; the woman who'd rung up my sale the previous night said someone had found the card in the parking lot. I'm not sure if it was found 24 hours after the fact or if the previous two guys had failed to notice its prominent position on top of a desk organizer on the counter, but I breathed a giant sigh of relief.
Conclusion: Add an anecdote for a lucky Friday the 13th and an unlucky Thursday the 12th.