I have, but I don't enjoy those. If I'm going to take a rest day, I want to be off my bicycle entirely and doing something completely different. It could be something active still, like hiking up a mountain ... but the bicycle is not involved.

That said, I will do 4 days of 80 km, then a day off, then a 50 km day, then 3 days of 80 km or something like that. I don't mind doing shorter days on the "ride days" ... especially if there's stuff to see and do along the way.