Yeah, I'm not trying to say you shouldn't use it for production use :)
They're opposing perspectives. As a user of arc I'd throw it into production. At the same time, from PG's perspective I'd want to be conservative about calling it production ready.
I suspect arc will never go out of 'alpha' no matter how mature it gets, just because PG and RTM will not enjoy having to provide support, or having to maintain compatibility.
 With some caveats: treat it as a white box, be prepared to hack on its innards, be prepared to dive into scheme and the FFI. And if you're saving state in flat files, be prepared for pain when going from 1 servers to 2.