Reading the Windows Live Writer wish list forum I have stumbled upon a request for a Word Count plugin. As the request has been done quite a while ago and there hasn't been any response yet I have decided to make one myself. As the solution wasn't that difficult I was able to stuff making it between work and personal stuff.
The plugin I have made works pretty simple: it grabs the selected text, removes any HTML elements (the string you get in the plugin method, contains the source view of a post content), decodes HTML entities and then makes the count using Regular Expression. It's the first version of the plugin and I might have missed some exceptions as I'm not a professional editor myself. Let me know if you have any suggestions or improvement/extension ideas.
I have already posted the plugin to the Live Gallery. Yet somehow I don't believe it's going to be available there really soon (the Find & Replace plugin still isn't by the way...), so I have put it at our CodePlex site as well.