Messages can now be sent via AJAX:
On any page on the site, you can now add a message button, which would
look like this:
<input type="text" value="sendMessage" onclick="displayMessage()" /> 
and the button will work

If you want to autofill the "to" field in the message, write your HTML
like this:
<input type="text" value="sendMessage" onclick="displayMessage('dan')"
/>
where the target username is the argument