Removing a misspelled word once it's been added to the spell check dictionary
You run a spellcheck, you're in a hurry and you accidentally mark a misspelled word as being correct. Now when you type the word, PowerPoint (and the rest of Office) thinks it's corrrect and no longer flags it as a misspelling.
I deliberately added a misspooled word (that one, in fact) to the dictionary, then went sneaking around behind Powerpoint's back.
In C:\Documents and Settings\MyUserName\Application Data\Microsoft\Proof I found a file called CUSTOM.DIC
This is a plain ASCII text file (ie, editable in Notepad, don't mess with it in Word or other word processors). I opened it and there at the top of the list was our new friend "Misspooled".
I deleted the whole line containing the errant word, saved the file, restarted PowerPoint and once again PowerPoint regarded Misspooled as misspelled.