I'm not planning to, but it came up with a friend who was saying she was totally grossed out by the idea of buying a used cup, and while I understood, I am pretty confident it could be made safe. Couldn't it?
EDIT: Just to answer some of your questions, I think my friend is just mentally grossed out by the idea of sticking something up her vagina that was in someone else's (who she didn't know) vagina. That makes this kind of an academic discussion at this point, as she won't be buying a used cup. I'm new to cup usage, but I think I have one that works for me (Diva) and hope I won't have to buy another one for a bit. However, when I do, I would consider used. I understand the initial mental gross-out factor, but, logically, I can't find that it's any less safe than sex (and by safe I mean likely to give me some disease the other person had, be it yeast infection or STD). Thanks all for your responses!