I don't think we've ever had out-and-out descriptions of sex; we generally do the 'fade to black' scene cut but I will answer questions of the 'hopefully we have a good time?' type. Sometimes, sex becomes a significant plot point or character development tool esp if it's that characters first time, or if it's a significantly good or bad experience; much more rarely the actual act itself becomes a significant plot point. It rarely gets acted on or asked about, but it's something I at least give a bit of thought to for major NPC's. What is the NPC's attitude, preference, experiences, etc; generally it's glossed over in a sentence or two, or it's something that flows naturally from other aspects of his or her personality.
I generally know my players fairly well and the limits that they will tolerate (which tend to be pretty broad). That said, if anyone has a problem, the problem is fixed quickly. That's only happened a couple times in my entire gaming career. With sex or anything related to it, I think it's also a part of being a good player or GM and having good taste to know when to create situations related to it or not. Know your group and their limits, and find out when you can - very occassionally (like, maybe, once or twice a year, if that) - push past those limits.
Graphic violence.. hmm. Most of our games are probably rated R. Call of Cthulhu or other horror-themed adventures: that probably goes up to the occassional NC-17 or beyond, strictly on the violence meter, but a lot of it is hinted at rather than described outright. Most of the times, I let them use their own imaginations and describe the reactions of others to the scene. (You put in the DVD you found at the suspected cultists house, the one with the suspiciously well-designed and sound-proofed basement. Ten minutes later, Hardened vice cops with 20 years experience are turning green and throwing up. Two pass out and one gets up, walks to the desk, hands in his badge and moves to New Zealand to raise ostriches.)