In the San Francisco Bay Area, I rarely have to worry about a frost, which means that I can leave plants out all year round without incident. I know that's hardly the case with readers living in the Midwest and on the East Coast, though.
Steve, over at Gardening Gone Wild, recently wrote, "I overwinter a host of plants in my cold dark basement. Every year I try new ones and am perennially amazed at what succeeds. Basically the idea is to trick a plant into dormancy, then keep it there. Cold — or at least coolness — helps. So does darkness. To survive, many plants need light, others need warmth, and some need both; those are NOT the ones I’m talking about here. For the basement, we need plants that can go into deep dormancy, a state of almost suspended animation."
I also know that Amy Butler does the same thing with her tropical foliage, which comes outside in the Summer, and then is tucked away in her basement in the Ohio Winter months. So, do you bring in semi-tropical plants or outdoor perennials when the temperature dips? Do you let them go into a state of dormancy, like Steve does, or do you keep them out and about?