Weird... I don't use Word 2008 that often but I've been using it more lately and I've noticed the exact same thing on both my Macs. Your message prompted me to try to get to the bottom of it, and after a little digging around I discovered that the file Word creates to save your own "creations" (words that you tell it to learn the spelling for) was missing on both my computers. Maybe the same for you? To check, go into Word's Preferences, then click "Spelling and Grammar". If "Custom Dictionary" is blank, like mine was, that's the problem. Click "Dictionaries", then "New"... etc., to define a new custom dictionary. After I did that I was able to Add words that Word didn't recognize.