What does it mean to be 'really' Jewish?

This article in Ha'aretz struck a real chord with me, as it's a question I spend a lot of time thinking about. Why is it that we concede authenticity to the visibly orthodox (i.e. chasidic Jews)? What does it say about our own sense of integrity as liberal Jews that, so often, we hold some idealized frum up as the 'real' Jew, or we exert all kinds of energy tearing that image down as if to cast the Shomer Mitzvot individual as some kind of religious Neanderthal?

This question came up again at Torah study this past week, even. What is 'mainstream' Judaism? The Judaism experienced in synagogues, JCCs, and other places of affiliation, or in marathons of "Curb Your Enthusiasm", pictures from Maccabi games on Facebook, and the Adam Sandler Hanukah song? Or does it even need defining?

So, I ask you: what does it mean to be authentically Jewish? Does it have to do with affiliation? With personal practice? Is it an ethical, cultural, or ethnic thing? Is it undefinable? Post your responses here (or leave a response when this gets posted as a note to my facebook)!

In the meantime, a happy New Year to everyone!