I haven't watched after 1:00 AM, but I know that Comedy Central bleeps swear words, but doesn't attempt to get their hosts to stop using them.. Jon Stewart and Colbert use "dirty" words frequently. So I assume they are NOT bleeped out after 1:00 AM on weekends. Why only the weekends? That's odd considering that more children are likely to be up watching TV on the weekends, than on weekdays.
By the way - it's kind of ironic that we can't use those words, here. But I assume Comedy Central, like our friends at Radio-Info; want to be polite, and deferential to the viewing public that might be offended. It's not the FCC - which, as I understand, has no legal control over non-broadcast entities like cable and satellite.
As for FX, you'll notice that their scripted dramas (The Shield, etc.) use the S word and the AH word, but never the F word. And you'll see those brief glimpses of semi-covered "nudity."
If you remember, NYPD Blue on ABC was the doing the same thing for the first few years of it's network run. Remember all the speculation about when the public would finally get to see Dennis Franz' fat wrinkly behind? There wasn't much controversy about it, considering ABC is a broadcast entity. But the FCC got way more conservative, and I think that both the show's producers and the public got tired of the gimmick.