This is cool!
At the bottom of every page is a link to a spell check macro. When you click it the words on the current page are compared to the words in LocalSpellingWords. (Before you go and click that link be aware that it is about 400K so it will take a while to load on slow connections.)
Take care when adding words to the dictionary as backup copies are made just like any other page edit, and multiple copies of that 400K thing will eat up space fast.