I've been training for three years, but still consider myself a newbie, and have followed the plan from Friel's book. I have usually taken a few weeks off at the end of the season (for me, last weekend) and then started with the base training. LSD with running and biking and drills for swimming. Usually my winters are sporadic and then I kick it into gear around March or so. I've done 4 races over 3 years and my times have not improved at all on average. I'm trying a new approach this year. I'm going to try to maintain my fitness all year by incorporating hill sessions and speed sessions along with the long runs and rides each week. In other words I'm not taking an off-season at all this year. I think my base fitness drops dramatically in the winter and I spend too much time trying to regain in late winter and into spring. I know this doesn't exactly address your question, but your post caught my eye after reviewing my first couple of years in triathlon. Good luck.

There's a couple of good articles on this site that address off-season.

http://www.slowtwitch.com/mainheadings/coachcorn/y2k.html

http://www.slowtwitch.com/mainheadings/coachcorn/downtime.html