hiya, i wrote a huge big reply earlier but for some reason it didn't post!!
anyway, the jist was that it depends when you go really. if it is the start of jan (until the 7th possibly) i imagine it will still be pretty busy, not as busy as august at all, but busier than low season (the week after the 7th).
however, I have spoken with Disney direct and they indicated that Jan is booking up very fast because of the Tower of Terror opening - they said that the Cheyenne is unavailable from the 14th-18th Jan (though perhaps just one of these nights is full).
I just booked sequoia lodge last week, so my advice would be to get your dates chosen as quickly as possible, wrap up as warmly as you would here if spending all day outside playing in the snow, and don't worry too much about the crowds - there may be many hotel guests but hopefully in Jan there won't be too many day trippers...thats what im hoping anyway!!!