tell application "Messages" to set status message to "On Mountain Lion"I'm pretty sure the beta didn't break backwards compatibility like that, and I really can't think of a good reason for it.
[kirkmc adds: It's true that the name of an application like this changes it should probably still respond to the old name. So scripters beware. It's worth noting that both Contacts and Messages do respond to their old names if you search for them in Spotlight, though Calendar does not.]

