btw, in the OP, you say that it's friendly if you wear a buttoned top. it's not about what you wear; it's about how friendly you come off as. if you joke around with your interviewers (professionally) during the interview, that's a huge plus. i remember my supervisor writing down during my interview that i'm serious yet i have a sense of humor (i joked around with the guys during my interview), and it landed me my current job.
spidey07: i'm a girl... i don't wear man suits very often.

however, i've seen how guys dress to interviews often enough.