Last year, the 2012 garden, I had followed some advice that it would be good to store the potatoes in the ground, under mulch, and that they would be fine until spring. So, in the fall I threw extra mulch (mostly hay and manure) over them and let them be. I dug some up in December and they were good. Then, I went out to dig more up in February, only to find that most of them had frozen. Some were no good at all, and some were ok, but tasted a bit sweet and had an odd texture. I cooked them all, mashed them, and froze them for future use. Gee...I've still got some in the freezer that need to be eaten! :)
This year, 2013, I did leave them in the ground as long as possible. However, last week when the weather forecast was calling for sub-zero temperatures, I went out on a crazy windy day, prior to the storm, and dug up the remaining potatoes. I think this was a good plan--storage in the ground as long as possible was better than storing in the refrigerator, and now that they are safely in the refrigerator, that is better than risking them freezing in the ground.
The Rio Grande Russets I planted were small, but good. The Yukon Golds were bigger and best.