I've read and been told time and time again that rest is very important. During the past year or so, my rest usually consisted of 1 day off, maybe 2, between riding.
This past week, I've been on the bike much less than I planned, but those 2 times I've felt so much stronger. It started with a light spin for an hour (and by light I mean heart rate ~ 120-130). I took Saturday and Sunday off. Monday I had a hard workout for ~3 hours. I took tuesday off and tonight was just going to be a light spin but the guys I was riding with (Haines point in DC) decided to attack on every lap, so I did a few laps much harder than I wanted to).
But bottom line, I felt so much stronger on Monday and tonight.
Finding the balance of pushing yourself and recovering/resting from those efforts is the trick to making progress. That's why now I don't get all depressed if I happen to miss a day....and there have been instances where I pushed myself a bit too much and ended up taking a few days off until I felt right again.