peacoben, FP, and Whaq... I have both UA ColdGear and the new FJ Baselayer, so let me give you the 411.
UA is definately warm, but as mentioned, very tight. In years past I've liked that because it made me feel "secure", especially helping my back in the cold. But as BHoll has said, it's warm enough to genrate a bit of sweat if the temps rise at all.
I got the FJ Base Layer as soon as it came out this year, and put it to use this fall. First, it is not as tight as the UA product in any way. It it what I would call secure, meaning it does not allow drafts to enter in around your arms or on your back. The shirts also have a longer tail length so that they do not pull up with a swing motion, allowing them to stay tucked in and not let the drafts in. The garments allow for easy motion and don't make you feel constrained. And as BHoll says, the moisture management is just excellent.
I purchased mine through TGW.com, and got both colors at the same time. So FP, get Mom or Dads credit card and you're in!