I found this response from a garden blog from the National Gardening Association that sums it up well: "If you have a very bright sunroom you may be able to overwinter them there. Some gardeners will root cuttings so that they have smaller plants to overwinter and then start cuttings anew in the spring from the by-then leggy plants. Other gardeners find that the time and effort and space are not worth their while and simply replace them each year. Good luck with your project!"

Here is the link:

http://garden.org/nga/searchqa/answer/14773/