Jackson was pretty young.... well, we were staying at my dads house about two nights a week at the time, and he was probably 4 1/2 months old when he got the whole downstairs with their dog. The upstairs has always been blocked off so the cats have their safe haven away from the dogs.
At our regular house (my moms), I have a whole "apartment" to myself (bedroom, living space and bathroom). Originally, he was kept in a crate when I left and at night but that only lasted a few weeks. Then he was kept in an expen for a bit, then went to being gated in my bedroom, then got full run of my entire side of the house, then by 7 months he had the full house (my side, plus the rest of the house which is fairly big). He spends most of his time in my bedroom though.
I think it depends on the dog. Jackson has just always been very trustworthy and he does not get into things when we aren't home (when we ARE home, it's another story
LOL) but when left and no people are home, he just sleeps. He's now 3 and it's never been a problem.