No, IIRC pg asked once and some people said they didn't want yet another messaging system to check.<p>Personally I think it would be great because a) not everybody remembers to leave contact information and b) you get the instant context and can forgo the "hey, I'm not a stalker but I thought you wrote something interesting on HN"
Those who want to be contacted should probably just leave their email address or preferred method of contact. It takes just as much effort to use an email client as does using a messaging system; the only difference is one would be checked on a regular basis, the other, not so much. Plus, as mentioned, people don't want yet another inbox to check. For those who don't drop a link to their homepage or list their email address, I just assume they're not interested in communication.
I would really like it, especially if it defaulted to "off", and you could set certain account age, karma, or karma-per-last-timeperiod thresholds for people to contact you. Even if messages just got forwarded on to email vs. a mailbox on the site.
Something like this would be really nice, even if it's just something like how Wikipedia does it: <a href="http://en.wikipedia.org/wiki/Special:EmailUser/Jimbo_Wales" rel="nofollow">http://en.wikipedia.org/wiki/Special:EmailUser/Jimbo_Wales</a>
(You'll need an account to visit that page.)<p>It sends an email on behalf of the user, and the recipient can reply back to the user via email (the sender's email address appears in the From: field.)<p>It works pretty well there, and there could be a karma threshold and a setting to disable it here on HN if it were to be implemented.
No need for a private message area.<p>But it would be nice if yc would email people on your behalf. Most people do not think of adding their email address to the profile area.