Some rules to follow that will make your situation much easier to deal with is the rule of three... for table service dining, there are three people you need to mention the allergy to...
1) The dining reservation agent (when you call 407-WDW-DINE to arrange for you meal).
2) The host/hostess (when you check in at the restaurant)
3) The server (when they actually arrive at your table).
Extra special / extraordinary (I don't want to say "unusual" but you know what I mean) requests should be overcommunicated as much as possible, perhaps even contacting the restaurant directly 24 hours prior to your meal (use the WDW switchboard # in my signature).
For buffet type meals, I have seen the chefs actually walk down the buffet line with a guest addressing allergy concerns for each individual item.