I made it out to Beverly this morning at about 6:45 a.m. and rode for about an hour. The ground was frozen and it was a lot of fun. It was my first time riding before the sun came up, so it took a little adjustment on my part to riding with a light mounted to my handlebars (which I think I will try to mount on my helmet, since I couldn't see where I was going in tight turns and had to slow my cornering speed WAY down). The frozen ground is like riding on pavement. There's as much traction as you could want. The banked turns on the south end of the park by the meadow were fun, I was hitting them harder (once the sun came up) than I did earlier in the year before it got cold enough for the ground to freeze. After the sun came up, it really got fun since I could see all the way through the turns.
I had to leave around 8:00, but the ground was still solid. It was kind of eerie, though, because as I was loading up my bike I could hear the ground and trees popping and creeking as the sun heated them up. I'm sure it would have been a muddy mess an hour or two later, but in the early morning it is pretty fun if you can dress for the cold temperatures.