(defadvice capitalize-word (after capitalize-word-advice activate)
"
  (unless
(or
(looking-at " I\\b") ; don't downcase "I"
(looking-at (sentence-end))
(looking at (line-end)); doesn't work, but I don't think \n would work either
(looking-at (user-full-name)) ; my name is a commonly occurring proper noun that should be immune to being downcased
)
    (downcase-word 1)))