In between Thanksgiving, Christmas, and New Years is a sudden rush of raiders that are going to be traveling, cooking, with family, or otherwise occupied. It happens every year, and every raid guild I've been in has had different tactics in regards to compensating for holiday lag. The most effective method I've experienced was a simple break for Christmas and New Years -- two weeks for raiders to eat, drink, be merry and refresh themselves for a renewed effort at progression upon their return. One raid leader I had spent a lot of time trying to make people feel terrible for actually having the temerity to make holiday plans. He didn't last long.
Holidays are supposed to be fun, and it's only natural that people are going to take time off from the game -- real life takes precedence over whatever happens to be going on in Azeroth. It always has, and it always will, and it absolutely always should. How does your guild handle the holidays? Do you take a break from raiding, or do you keep right on with progression content? Do you drop progression in favor of fun events? Do you take those raiders that are still around and go back through old content and old achievements? How do the holidays effect your guild, and how do you compensate for the annual very merry lull in activity?