I need to get everyone's opinion on this one. I have the opportunity to take about a week off and visit Madrid in late December. It would involve leaving around the 27th and returning around the 5th of January.
Here is my question. Is this time of the year a good time to be in Madrid?
I've never been to Spain that late in the year and was wanting to hear suggestions and thoughts. What will the weather be like? What would be some good things to do in Madrid in the winter?
I've also heard there is a huge celebration in Puerta del Sol during New Year's Eve. Has anyone been there?
Is the city extremely crowded then? Any suggesstions on places to stay?

Thanks for your help.