http://www.gaijinpot.com/
this forum would help you out a lot as it's essentially a collective forum of foreignors that (im guessing) mostly teach english or are students in an exchange program.
the majority of what ive read on that forum dictates the sacrifice a foreignor has to pay to live in japan. not only is the cost of living high, but the livability is low (given there's barely any space to do anything, anywhere) and the pay sucks. in addition, if you're a visibile minority in japan (eg, you dont look oriental) then you're going to deal with racism. but hey, dont take my word, or any of these forum members word for it. go out there and experience it!