Given that many of the people I know use Facebook messaging for the sorts of personal messages they used to use email for, this new policy is very much like Google allowing mail senders to pay them to bypass their spam filters; I know Facebook's got to make money, but I'm not terribly impressed - it used to be that only people I was friends with could get into my inbox.
I'm not sure its as easy as the post makes it sound, the person not having a facebook account would still need to provide identification, otherwise, if its a facebook user, he can be reported for spam/blocked/banned or something.
or thats what I hope
I suspect it'll mostly be crappy Farmville clones and big corporate pages trying to do "social marketing", but we can hope...