csi56: I know all a bout the 'rubber leg' problem--at least I USED to. After reading Friel's and a couple other books on long distance cycling, I got into better nutrition. Not a big meal overhaul, but eating enough while riding, making SURE I was getting enough electrolytes to replace what I sweat out, and IMHO the MOST important thing--getting a high carb/protein drink in me WITHIN the first 30 minutes after a hard effort.
I did a full century in early May, and even though the first 60mi or so were into a 18-25mph headwind, made it in 9hr 10min overall--about 7hr 40min riding time. Unlike a similar century a couple years earlier (before the better nutrition), I had no 'rubber legs' and was able to start riding a couple days later. Still had a bit of 'sore butt', of course!