I think that "as" can have the same meaning as "but" or "However". For example: "My friends love nothing more than going out clubbing at the weekend. As for me, I prefer having a quiet night in with a good book." "For me" on it's own would be a non sequitur (following on from nothing in particular) and an attempt to define something. e.g. "For me a quiet night in involves reading a good book." Hope this helps. David