I'm in Venice (have been for more than 28 hours) and I so much love this city in winter, especially December. It's been gorgeous weather, at least from a New Englander. It was a high of 55 yesterday and 52 today, both days sunny without wind. The nights are cool but not cold, and as my hotel is on the lagoon, I am leaving my windows open to get the sounds of the sea, which I adore.
I can honestly say while I have been treated well at many hotels, no one has ever treated me as I have been at the Londra Palace. The fact that the reserved a whole terrace for me (not just a balcony) over the gondolas at San Zaccaria even though I had to change my reservation at the last minute is even more impressive. Everyone here is treating me like an honored guest, which I really appreciate since it's part of no hotel chain I am a member of (though I booked and changed through hotels.com) -- its a Relais & Châteaux. I've already eaten at Do Leoni (one of the best restaurants in Venice, at the hotel, once, and will do so again since it's so good).
Venice is so beautiful this time of year. I once again walked straight into Basilica San Marco without a person in front of me as well as La Fenice (I'll have some new photos of that), and it feels like Venice as it should always be. I did stop on the way back to the hotel today to get some diet coke (a habit even worse than red wine for me ) and the man was literally shaking (it was 50 degrees!!!!). He said he was molto freddo (very cold). I said I was fresco (nicely warm) since I come from New England. He was astonished. He went on to say how much he hated Venice in winter while I said I loved it so much more. An interesting discussion.
So I guess if you're from Miami, you won't like Venice in winter. If you're from the Northeast, it's heaven, great weather, and almost no tourists.
BTW, I'm sure this is big news in the US, but it's been all over the European news channels -- all UK airports were closed for a few hour period today because of what they are saying is a technical glitch or human error but are not ruling out something worse. Some flights are now in line at the various airports, but BA and others are offering full refunds or rebookings. It's being taken very seriously in Europe.