RE: sending gmail messages -- Search the wiki (or Google) for gmail and how to send email with VC.
The caveat is that open dictation is not very reliable, particularly if you have a poorer quality microphone, background noise, or a "non-standard" accent. (And, of course, for those VC2 users who are using the alternative speech recognition engine, dictation is not an option.)
As far as facebook is concerned, I don't have an account so I can't help much with that. If you can have Facebook PMs automatically forwarded to your gmail, that would be the most obvious solution for getting them read aloud to you, I should think.
