In which D'oh! is first revealed to the groups as the canonical spelling:
http://groups.google.com/groups?q=+%22d%27oh!%22&start=100&hl=en&scoring=d&a s_drrb=b&as_mind=12&as_minm=5&as_miny=1989&as_maxd=1&as_maxm=12&as_maxy=1991 &rnum=129&selm=JYM.91Apr5213437%40remarque.berkeley.edu
on 4-6-1991
and I believe it's the first "D'oh!" I've spotted. There are an uncountable number of them typed daily now, of course.
john . Bergmayer