I'll take about 3-4 weeks complete off before starting up again with winter training. First phase is lots of base miles on the CompuTrainer followed by segments of strength and technique drills with intervals. Towards the beginning of the season, I try to get a way for a week or so of some outdoor riding where it's a bit warmer. That incentive keeps the drive thoughout the long boring winters.
I also do quite a bit of downhill skiing, but that's just for fun, so no serious cross training... although it does build legs strength.