What an interesting thread! I train at a karate school in western Japan and we use ossu A LOT ( ossu is the standard romanised spelling). If we say `hai` to my teacher or any other member of the club we get told off and told to say `ossu` instead. We are not allowed to say `hai`. We also use ossu as a greeting and say it before and after sparring. I`ve never been told it`s rude before, in fact in my dojo it`s considered the norm. We even have to use it when we send e-mails. I have occasionally heard it used on the street and on TV, mostly between guys and it doesn`t seem to have caused offense. However, as was said, Okinawa is very different from mainland Japan and the language is very different, so the rules there may well be very different too.