Do you have a work hubbie?

Lately, I have been hearing the term "work husband" more and more frequently, now what does that mean exactly? Most people define it as someone you work with who you confide in about work, among personal issues and all sorts of other things, usually of the opposite sex. The question is, when exactly does confiding in one about personal issues including sex and relationships cross the professional boundary line? Is it okay to have a coworker with whom you discuss topics you would usually only bring up with your best friend? My opinion happens to be, watch what you say to those you work with, you never know.