Is it just me? Up to three days is OK. By the fourth or fifth day of wearing unwashed jeans, they feel really itchy.
It's a mostly moot point for me anyway though, as I've usually gotten them dirty by the second or third day anyway.
@JeremyS - I quit after two weeks as I thought my family might think I've lost my mind. I had no complaints from anyone over smell or that I was wearing them so long. In the end, I thought the two weeks was enough and I should wash them. With my latest pair, I'm going for at least two weeks again.