Cat at Beyond Books posts about urban fantasy authors all knowing each other. She names Kelley Armstrong, Kim Harrison, Melissa Marr and Vicki Pettersson as members of the ring. Yes, in fact many of them do know each other, though they didn’t meet prior to signing book deals. The meetings came as a result of the deals and out of defense of having penned something that didn’t fit with anything else. There just wasn’t a wealth of experience to draw on, so the authors contacted each other, connected and helped each other out, becoming friends in the process.
Also, the authors named don’t blurb books they don’t like. So you know you’re getting a good story when you see a quote from one of them.