MDG- what i said was that ivrit was the only language not in existance when rashi lived, and therefore, the only one he couldnt possibly have spoken. i wasnt saying he spoke yiidish.
Avi k- ive heard many choshuve roshei yeshivos give shiur in english and hebrew, and they frequently switch to yiddish to say the crux of a vort. interestingly, a friend of mine in kby (gasp) told me the same thing, and constantly uses yiddish to better make a point while learning. i think you just have an agenda.
zdad- uhu.