I feel that there are pros and cons to utilizing a social network for both sending and receiving messages. Facebook is a very multifaceted social network. It affords the user the ability to observe, interact, and provide feedback through various platforms. Sending and receiving messages is one way in which a user can interact. Messages can be sent live via instant messaging, or in writing, via wall posts and direct messages.
One of the benefits to using Facebook for the purpose of sending messages is the direct connectivity it offers. Facebook enables me to find people that I am currently interacting with, have interacted with in the past, and people or businesses I might find potential interest in. Even if the other person/business is not a member of my subscriber base I still have the option of reaching out to them through a written message. Locating contacts via an open search engine such as Google involves far more research, and can be time consuming. Receiving messages via Facebook is comparable to receiving an email. It's very simple to access, and the marketing junk mail frequently associated with email is a non-issue.
The cons to receiving and sending messages via Facebook? Hmmm... maybe the fact that you have to log into your Facebook site for retrieval. Facebook sends a notice to the email address of your choosing alerting you to the fact that you've received a new message, but you still need to access your Facebook account to reply. The same applies to sending a message: you must navigate to your Facebook account in order to send a message. The negative or downside: major distraction. I get sidetracked far too easily, and avoid Facebook unless I've got extra time to spare!