When I have purchased expired domain names in the past, at least in cases where I know there was a previous web site associated with the domain, I would use a disclaimer such as "Not affiliated with the previous owners of this domain."
In another case, I avoided purchasing a domain name and web site where the previous owners had made a bad name for themselves. I didn't want to link my sites to that kind of negativity.
Yesterday, I was searching for something entirely unrelated, not looking for domain names at all, and happened across a domain name that coordinates with my main site's domain name quite nicely.
The company had folded, which I read in a couple trade magazines. Some of their other domain names were now in the hands of some of those companies that grab expired domains to draw users to their search directories. But, this one particular domain name was unregistered and available. So, I grabbed it. ;-)
But, I am curious as to whether there is any liability with using the domain name of a folded company? From what I read, it sounds as though they simply folded and were not sold to another company. And, even if they had been sold, the fact that this domain name is unregistered for who knows how long now, would seem to indicate that any new owners don't have an interest in the domain name.
So, on the one hand, it strikes me as fair game. But, on the other hand, it's surprising that no one else had already grabbed it.