I often write what "sounds" right (being not a native English speaker/writer), and I believe the expression "that being said" to be fairly common, as opposed to a more complete form like "that's been said" or "Having said that".

In doubt, I turn to google fight, which seems to confirm the common usage. (not exactly the right reference, I know.)

Yet, I don't think that "that being said" is correct, especially in writing. "That said" is even more common. Is it also acceptable in writing?

What expression would you use in formal writing? (Not too formal though: like a technical forum)