OK, Mary - let's ask people to post information about camps and such here, and see where it goes.

The San Francisco Folk Music Club has its annual Camp Harmony during the week after Christmas, in the mountains outside Santa Cruz. Cooking is by the charming and talented Debby McClatchy (and Joe Offer was rehired today as Chief of Kitchen Cleanup). If you register before November 2, Cost is $250 for the 5-day camp, $170 for children.
I can't find the sheet that has the dates for the camp, and the newsletter in my hand doesn't give dates. It always ends on New Year's Day after a fabulous New Year's Eve celebration. It's a five-day camp, give or take a day.
The Website won't help you at all - it hasn't been updated in years.

Thanks to Mudcatter Charlie Baum (and others), information for the annual Getaway of the Folklore Society of Greater Washington is easy to find online. Charlie says the dates are:

Friday October 18, 2002 through Sunday October 20, 2002 (and even into Monday morning, October 21, 2002) location: Camp Ramblewood (Darlington, MD) [near Havre de Grace]

This camp has become the unofficial official annual gathering for US Mudcatters.

-Joe Offer-