I'm not disputing the fact that men in our society "care less", on average, than women about whether the house is clean. But let's think about why this might be? Messy male commenters, what did the house you grew up in look like? Were the common areas messy? The bathrooms gross? Dishes festering in the sink? Did you turn your underwear inside out for a second wear? If the answer really is yes, then you probably came by your slobbishness honestly. I would actually be willing to bet, though, that people brought up in a house like that had some family problems besides chores division, and are likely as not going to rebel by making things in their own homes perfect.
If the answer is no, why wasn't it messy at your house? Again, the answer could be: I was raised by my single dad and we all chipped in, and while it wasn't white-glove clean it was fine. Again, though, if that's the answer I bet you are not one of the truly slobbish.
I think the most likely answer is: my mom picked up after everyone, although my dad and I had chores of a typically masculine kind such as mowing the lawn or raking leaves or making dad's special waffles on sunday or whatever. I was nominally responsible for cleaning my own room, and I had to be harassed to do so, and my mom actually dealt with the laundry side of things. Or, everyone had chores of an load-the-dishwasher type and for the heavy stuff we had a cleaning lady.
[I should note, here, that it is possible for men to be unfairly overworked if the "guy" chores happen to be very demanding, as when you have to use a snowblower all the time, or split wood, and there's no reason why women can't rake leaves.]
Now, as to the fact that men living alone are often slobs, we have to ask when and where this is. College apartments? Everyone is a slob in college. How do men who have lived alone all their lives generally do in the cleaning stakes? Any of you know any 50-ish, never married men? All the ones I've ever known had really, really neat houses. What about widowers? Unless their wife just died and they are suffering from depression or something, again, neat. Guys in the military are not known for their cavalier attitude towards matters of neatness, are they?
[UPDATE: This post wasn't actually done; I meant to save it to drafts...]
My point is just this: guys do not have magic blinders on that make them unable to see dirt. How can we tell? Because when household or employment structures demand it, they can see dirt just like a regular person. My step-dad was raised by a very strict father who was a colonel in the Army. He actually used to make white-glove inspections where he ran his gloved fingers along the edges of the upper shelves of the bookcase. Penalties for failing were, um, strict. Oddly enough, my step-dad was able to see even small amounts of dust, even on lampshades. (The effects were not life-long, perhaps...)
It is easy to see basic game theory at work in the putative all-guy household; it is rational to maximise your tolerance of mess because whoever is the least tolerant will do much more of the work. I think all my "guy's are just messy" commenters will aknowledge this. Why, then, not think that in the two person, mixed-gender household the same dynamic is at work? It is rational to dip slightly below your set level of caring about dirt, because then you will do less work, and the house will likely be as clean as you wanted. This doesn't mean men are all manipulative bastards or something, except insofar as everyone is a manipulative bastard. It just means that if they go with the flow, conform to the percieved stereotype of not seeing dirt, and generally follow a path sanctioned by society, they will reap some real rewards. The fact that internal pressures will make their wives or girfriends feel that the messy house is in some way "their problem" doesn't get these guys off the hook. I just don't believe that people magically do not notice when the bathroom smells bad. I think when they say, "I just don't think it's dirty" they are saying, "I don't feel like doing anything about it right now and if I put it off just a little more, I may not have to do it at all." And don't pretend that guys never purposefully do a really half-assed job so that they won't have to do it again. The flip side of "she's never satisfied with how I do the dishes" is "he doesn't wash the bottoms of the plates!"