I'm not sure I like this line at all I'm afraid Top; while black is certainly better, I hardly think this punishes white for his petulence enough. On the other hand, I suppose that white's tattered pawn structure means he has virtually no winning chances and would have to grovel for a draw, which makes it a perfect choice for those who are happy to rely on their technique.
The "approved" refutation (if not a particularly convincing one) is 1.e4 e5 2.Nf3 Nc6 3.Nc3 Nf6 4.Nxe5 Nxe5 5.d4 Ng6 6.e5 Ng8 7.Bc4 d5! 8.Bxd5 c6!, which allows black to hold onto the piece with not too much risk. The point is that in many of the lines, white gets too much compensation by getting a pawn wedged in on d6, and then has all sorts of threats. By playing this line, white's only compensation is the strong centre, which will first be fixed by playing ...Be6 (after Bxe6 fxe6 the pawns are going nowhere, and the open f-file often comes in useful for black), and then dismantled by a later ...c5, usually after ...Bb4. However, all of this is a little messy and I think that 7...c6 8.Qf3 d5! 9.exd6 Be6, as recommended by Cordel many moons ago, is an even simpler way to a comfortable advantage. http://www.xs4all.nl/~timkr/tour/breeze.htm
is Tim Krabbe's well-known article on the opening, and on it there is a lot of analysis.http://www.jakob.at/steffen/halloween/index.html
is another site on the opening, by the creator of the ICC program Brause, which scored incredibly highly using the gambit, and encouraged an army of blitzers to take it up for themselves, myself included!
It's a shame I play the KG, or I may well have trotted this out OTB on a few occasions - underestimate it and you shall surely perish, and perish quickly!