We stayed there last Christmas and I remember asking exactly the same question then.
It was fine though - we left the heaters on throughout the day and so it was lovely and warm when we got back
Same for us, we went in Feb and if you left the heaters on during the day it was fine when you got back. BUT queuing for breakfast in the morning was NOT fun in the frost for up to 30 minutes.
We stayed there in January 2008 and 2007, I agree with everyone else as long as you keep the heaters on you will be fine. It snowed when we were there in 2007 and the ranch looks lovely in the snow. One word of warning though if you do plan to go swimming while your there, the water is very cold, it is heated but for some reason it feels freezing, either that or we're just wimps.
Ok I think it must be just us then as dp and ds2 never seem to have a problem, but myself and ds2 only last 15mins before we have to go and sit in the jacuzzi and warm up.