One issue we’ve encountered with copying and pasting from Microsoft Word into Mozilla Firefox 3 is that it brings with it a whole load of Word-specific code, e.g.:
<!--[if gte mso 9]><xml>
<w:WordDocument>
<w:View>Normal</w:View>
<w:Zoom>0</w:Zoom>
<w:PunctuationKerning/> ...

which can lead to unexpected results on the published page. Even using the “Remove all formatting” button doesn’t remove the unwanted Word-generated XML code.
PureText
However, I’ve discovered a small Windows application called PureText by Steve Miller that runs in the system tray/notification area that addresses this issue.
The application runs as a single executable file (i.e. you don’t need to install it) and when you’ve copied your text from Microsoft Word, rather than pasting it with the standard Ctrl+V instead you use Windows key+V.
This effectively does the same as pasting the text into Microsoft Notepad, then selecting it all and copying it out again, removing all the formatting in the process.
My initial tests have been encouraging.
Gareth @ St Andrews