Have you ever been irritated at the way loads of Windows apps insist on using RTF or HTML when you cut and paste text? I have.
For example, you want to copy something in Internet Explorer into your Word document. You end up with a whole bunch of stupid fonts and formatting. It might be useful now and then, but mostly it's just not what you want.
To get around this, I used the fact that generally the applications from which you copy/cut text can make the clipboard available as plain text, in case you are pasting into something that doesn't support RTF/HTML. I hacked up a little app that requests the clipboard as text, and if it's available, copies it and makes it available only as text.
The source is here, and is free in all senses. An executable is available here if you trust me.
Now, copy text from Internet Explorer, run the app, then paste into Word. Magic! - only plain text gets pasted in. Apparently this is also useful if you paste into an HTML email composer, but only a cretin would be sending HTML email :)