exhaust question

alright im thinking about gettin a motorcycle maybe wait a year and get an 07 cbr.. those seem to be worth it but i just read recently that bikes with exhaust under the tail, the exhaust fumes somehow stay up near the rider and stink?? and in this case give this rider headaches.. is this a common problem with other people or not?? also would it be a big enough problem where id be better off getting a bike with a side mounted exhaust?