I got first dibs (or something like that) and decided to run Call of Cthulhu, because Erik has always been the Keeper and never actually got to play.
I thought I was ready. I wasn't. I'm familiar with the rules and mythos, but running CoC is an entirely different monster. I ran a scenario (A Little Knowledge) from one of the older editions of Arkham Unveiled. I spent a good portion of the night figuring out how to get a librarian, a parapsychologist, an artist, and a psychiatrist together. The first two were characters who'd previously investigated together, so no sweat there. However, I just seemed to flounder in my attempt to draw the other two in. This has lead me to believe that an interesting and useful Call of Cthulhu scenario supplement would be one that focuses on bring characters together in the first place.
We didn't finish the scenario last night. We'll finish it next week. I'll leave you with some of the better comments and quotes from the night:
Me: "Make an idea roll."
Steve: "I succeed."
Me: "Okay, you just really want to shake the hell out of her."
Me: "You've even heard rumors that she even dabbles in the black arts."