What proofs for refuted gambits are there? I've stumbled upon this article a while ago, and I've also seen refutations for the Muzio Gambit (Joseph Kling &amp; Bernard Horwitz - Chess Studies on Endings of Games). I'm wondering what other gambits are proven to be unsound.

Edit: I'm looking for refuted gambits in the strict sense of the word, followed by proof. Even though a gambit might be playable against someone who doesn't know its refutation, the gambit is still considered refuted if it is proven that the side who initiated the gambit loses in all variations worth looking at against best play. So yes, I'm looking for scientific proof.

Also, if a database of almost all games played in a particular gambit shows that the side that initiated the gambit wins almost all the time, this doesn't mean that there isn't a way for that gambit to be refuted, it just means that if there is a way, most people haven't played it.

Above everything, I'm looking for material to learn from. An article that says that Vasik Rajlich or someone else has used a computer cluster and came to a conclusion regarding a certain position, how will I benefit from it if there is no proof? (And please note that that King's-Gambit-busted-by-Rajlich article was in fact a Chessbase April Fools' joke!)
As long as chess can't be calculated from beginning to end, it is very hard to scientifically prove an opening to be refuted (aside from lines that leave you with such hopeless situations like a bare king against king and rook, of course).

If you are satisfied with a less scientific proof, I'd say gambits are even less so refuted. In my opinion, nearly all gambits are playable, as long as you won't play it against a superhuman database/program or a world champion. In a practical sense, probably no gambit worth of having a name is refuted in the sense of not being playable. Even if a gambit is widely considered unsound and often results in a worse position, it might contain enough steam to give your chess skill ample opportunities to overpower your opponent.I even remember a game where I suffered terrible against the BDG because I didn't find any refutation over the board. I only won because my opponent terribly misplayed the late midgame, but from the opening point of view he should have won the game.

So my answer is: No gambit I know of is refuted to the degree of being unplayable.