This is my first year living aboard in winter. Soundbounder mentioned my blog earlier in this thread. I've moved a few times, but am settled now in one location for the rest of the winter. A few things about the above comments, and my experiences:
1) Condensation will be the biggest problem. Temperatures drop outside and its toasty warm inside. One thing that helps, but isn't perfect, is a lot of insulation and bubble wrap on the inside of your hull. The condensation on my port side is worse than my starboard because it gets hit by the wind more. I put everything in my lockers in plastic bags, just in case. And now I check the lockers frequently. Other solutions: dehumidifier, constantly running fans, etc. I couldn't afford. All I did was insulation, bubble wrap, and plastic bags. Its ok so far. I mentioned the condensation problem only once on my blog and people still post comments with lots of suggestions.
2) Yes, there are places to liveaboard in the winter. And its waaaay cheaper than in the summer! A bubbler is a good idea, but as some suggested, it may not be necessary. Double check with your boat insurance company. Sometime they won't insure the boat in the winter without the bubbler. In MA? I have heard that Boston has a great community of liveaboards, but I haven't ever checked it out.
3) About the cover. There are two posts on my blog with pictures of my cover. Mine is a great one...almost a custom fit. Its a wood frame with a giant piece of canvass over the entire boat. It helps a lot with keeping warm inside and keeping the snow off. My cockpit is much warmer because of it.
Sailing, Simplicity, and the Pursuit of Happiness