When signed-in, you will see a link for My Message Board in your toolbox.
You can use personal message boards to ask someone to clarify a question, thank them for an answer, tell them you like their contributions, ask them something about themselves, and welcome them to a WikiAnswers topic you're active in.
To communicate with someone else you post a note on their board. When someone else wants to communicate with you they can put a note on your board.
You can access someone's message board from their Profile, which is linked from their username anywhere it appears.
For example, if you click on the Discussion link in the toolbox on a question you will see who has contributed to it. You can click on any username. If someone posted a note on your message board their username will be linked there.
Unfortunately, anonymous contributors — identified with IP address numbers — cannot be communicated with using message boards.
Once on a message board, simply use the form at the top of the page.
Please, please, please don't post questions and answers on personal message boards.
We have been carefully improving our WikiAnswers system to maximize the public benefit that can be gained from personal Q&A and other interaction.
By asking, answering, and improving Q&A on WikiAnswers you are growing permanent information resources for the entire world. If you post comments on bulletin boards you're just communicating with that one individual and your contributions will eventually disappear.
Note that these are "personal" but not private. They are made for personal communication: one-to-one messages as opposed to one-to-many and many-to-many questions and answers. However, anyone can read anyone else's message board. Don't write something you want kept private.
Someday we may add a private messaging system. In the meantime people may choose to post their email address so that others can communicate with them directly. If you choose to do this we recommend that you format it in such a way that it doesn't look like an email address. That way the spammers are less likely to find it.
Do you have other questions about using Message Boards? Email WikiAnswers @ Answers.com.