There wasn't, but there is now.

When logged in, above the post box you'll now see a PM button that will let you contact the post's author. You'll also see an Inbox button in the top section by the Profile and Logout buttons where you can view/reply to messages. And if you click the Members button in that area you'll get a list of the site's members; in the Member Actions sections for each there is now a button to send a PM.

By default, the message will go to the member's inbox here and that member will also receive an email notification. Members can opt out of receiving email notifications, and the whole Private Messaging system, by going to Profile > Options.

I had been hesitant to activate this feature for a variety of reasons related to potential abuse and spam. If problems arise or it creates an undue support burden it could easily go away. But I think we have a good community here and am willing to give it a shot. So enjoy!