Best Least Known Windows Feature

 I don't know where I learned this trick, and since learning it I haven't seen anyone else use it - so time to spread the knowledge.

Windows will copy the text of a standard message box to the clipboard on Ctrl-C.

That means you no longer need to mail an image like this:

Instead you can get

---------------------------
Error
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file:///C:/Users/sw/AppData/Local/Temporary Projects/SampleMsgBox/bin/Debug/SampleMsgBox.EXE
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OK Cancel
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Which is really great for those long file names which you have no chance of remembering and little interest in typing.