I have managed to overload Microsoft Word's spell-checker. 281 pages into this document, I got a message saying "There are too many spelling and grammar errors for Microsoft Word to continue displaying them." It's not that I'm a bad speller (or a prolific writer), though. The document was a compilation of news stories copy-pasted out of Lexis-Nexis for a project. Since they were news stories, I must assume they were all spell-checked extensively, which means the errors that Word was getting overloaded with were just unusual last names.