Just wanted to add my tuppence worth: in the first few months of marriage I found out my husband was subscribing to FHM. Now he KNEW how I thought ANY porn, pg 3 girls, FHM, etc was despicable (he'd binned his porn collection when we were going out when I found out he had one and kicked off!). Completely against my principles. Anyway, the magazine came through the door - I cut out every topless/naked girl...there wasn't much left of the magazine. I then replaced the photos of us in frames around the house with said naked cut-outs. He came home and we had a blow up. I made it clear that this was a big no-no for me. He cancelled subscription and apologised, never again, bla-bla.
Year or so later, I find dirty images on his computer - big blow-up, I go off to my parents, he apologises like a dog with his tail between his legs, thought I was going to divorce him. I make it clear that next time I will.
Fast-forward a couple of years...me breastfeeding newborn surfing net on his computer...and the screensaver is some girl 'pleasuring' herself. We had company at the time, I glared, he jumped and grabbed laptop. I don't recall fighting about it. I probably felt sorry for him with tearful wife not at all interested in intimacy.
Next incident...well, I find a particularly 'stained' pair of underwear in his study. I left it on his laptop to let him know that I'd found it. He didn't mention it, I did, but it didn't blow up, just a cold disgusted shoulder from me. Clearly the time I thought he was playing computer games (which also annoy me but another topic), he was actually seeking comfort from the girls on screen.
Bottom line...I don't trust him, I think he watches porn as much as he can without me finding out, but as I am not really bothered by sex (as in don't really want much, once/week more than enough), I figure he needs some stimulation somehow. It still disgusts me and somehow I have to drive this zero-tolerance through to my son. But for me, not worth ending our marriage over and in a way, I feel myself to blame due to lack of my libido so don't feel I have grounds to end marriage. Plus now with kids...I couldn't do it to them. They adore their daddy.
Not sure this helps, but gives some perspective to what others out there have experienced.