I have no idea what Emory or USC are like. Those be in drivin' cities - I hate driving.
As far as transferring goes, there were a couple people that transfered out last year. It's pretty much pointless to transfer though, because the schools above BU aren't going to get you much futher. To teach, you're probably going to need to go to Yale, Harvard, or Princeton. It's doubtful you'd get into those from BU even if you were #1 in the class (otherwise you'd have gotten in in the first place, or at least gotten into somewhere a little more competitive - they still look at your LSAT and what not). For other jobs, it's not going to make that much of a difference to go to a slightly better school. If you did well enough to transfer to a better school, you're probably in a fine position to get a good job based on your first year grades. If you transfer, you gain nothing, but you'll have to move away from your new friends and you might not be able to be on a journal. There's really no point - but yes, you can transfer from BU and maybe even to someplace better.
Who are the "student ambassoadors"? Are they current students? If so they'll probably tell you anything you want to know. I don't think people get paid for those tours. (We do get paid for calling people.) In any case, no one really has much to gain by witholding anything about the school (unless the Dean is standing right there). They'll tell it like it is.