This is definitely one of the strangest problems I've encountered in OS X. Using Mail.app when writing an email, I type a sentence and at the end of the sentence I type period and then hit space before starting the next sentence. When I hit space a second period shows up after the initial one folowed by a space. If I hit period wait a few seconds then hit space it still double punctuates. If I wait like 10 seconds then it doesn't happen. It only happens immeadiately after a word. If I type a random period it doesn't happen. After quite a bit of testing I've noticed that it happens with ANY punctuation, be it period, comma, semi colon, colon, dollar sign, number sign, carrot, anything. It doesn't happen with safari, word, AIM, or Adium. But it happens with Mail.app and I've also seen it happen with Adium's Crash Log app. I've also noticed that Mail.app has now stopped spell checking as I write. I checked the preferences and the box is checked to check spelling as I type. I'm using a Logitech MX700 keyboard. I thought it might be the keyboard, but I tried plugging in an apple pro keyboard and the problem persisted. It's got me completely stumped. I hope you all can understand my explanation. If anyone has any ideas I'm all ears. Thanks.