<p>This has been discussed ad-nauseum on Meta Stack Overflow (where Stack Exchange itself is discussed) and has been declined (several times, if I recall correctly).</p>

<p>See <a href="http://meta.stackexchange.com/questions/431/any-way-to-send-a-personal-message-to-another-user">this question</a> on MSO for excruciating detail.</p>