I love going in January too. As the above poster mentioned, the only downside is the weather is so unpredictable. Last January it was beautiful the entire week we were there, upper 70's/low 80's and no rain. The year before however was freezing. We wore our winter coats at night for a good part of the trip.
Makes packing more difficult, as you essentially have to prepare for any extreme, from shorts and t-shirts to hats and mittens, but the lack of crowds more than makes up for it.
Have a great trip!