K.V.
I think many men do this (and probably some women), however i would not want to see this on my computer and know what my husband was looking at. I would tell him up front that it makes you uncomfortable and since it is a shared computer than he needs to either a) buy his own private computer b) find another way to indulge himself. C) Learn to completely cover his tracks so you never stumble across it again on the computer d) stop.
There are some things that you just have to accept (to a certain degree) but at the same time, there are some things that he should be more descrete about.