My reason for asking the question was because when I bought a new pair of jeans on Thursday, the man in the shop started telling me how to wash them. I replied "people wash their jeans?" He smiled and said something along the lines of "oh good, you don't wash them, that's how it's supposed to be". We then had a discussion about washing/not washing jeans and he said that it's less hassle to give people basic washing instructions than try and explain why jeans shouldn't be washed unless absolutely necessary.
The 501s I'm wearing now haven't been washed since I got them which is just over seven months and the new pair I bought last week won't be washed either unless they absolutely need it.
They don't smell, they're not disgusting and the only way you'd know they haven't been washed is if I told you. Which I just have!