I read with amusement a couple of weeks ago Bill Hartzer's article on advertisers who bid on 'keyword', simply because they've included the header row when they copied stuff out of Excel. Here's another example of the dangers of Excel that I found on Yahoo for 'private medical insurance':
Whoops! Using a formula to create customised ad copy is a great idea, but you've got to watch for mistakes. The #NAME? error usually happens when you misspell the name of the formula itself.