I disappear for a little while, and all heck breaks loose... No further comments from Empty yet?
The line after 5...Be7 all the way to 12...Be6 has been debated in here previously I believe, and is discussed briefly in Monson's book on the opening. He gives 13.Rd1 += with no further analysis. Following dragonmaster's analysis below, we get 13...Bxb3 14.axb3 Re8 15.Qxd6 Qxd6 16.Rxd6 Rxe4 17.Be3 h6 18.c3 Bg5?! 19.Bxg5 hxg5 and now, instead of Kiss's 20.Kf1, I'd be inclined to say that 20.Rd7 is a stronger move, although it is still equallish. I would concur with Schroeder that, whilst the position might be objectively equal after both 15.Qxd6 and 15.c3, white has ample scope to play on in a simplish position with almost no losing chances and a few chances to pressure black. If this is the best black can manage against the BG then the gambit is very much sound. I agree further with Markovich that 7...Nxe4 (or, indeed, 5...Nxe4) is the critical continuation.
Monson also mentions 13.c3, though then he only considers the erroneous 13...d5. 13...Bxb3 is indeed stronger, but after 14.axb3 Qe7 15.Bf4 Rfe8, 16.Bxd6?! is probably not strongest. Better is probably 16.Rfe1 with the idea 16...Be5 17.Be3 intending a later f4, which is a thematic manoeuver in this variation. Does white have an edge? Probably not... but again, in practice he probably has the better winning chances as black will find it difficult to get in ...d5, and sooner or later white will be able to organise his pieces efficiently. I'm not saying, with best play, he should get anywhere... but if this is all black can aim for against the Belgrade, some pseudo-grovelling, then white has nothing to fear.
I have never lost in the Belgrade gambit in a serious or semi-serious game (I did lose one quickplay 4NCL game a few years back, but even then I had a winning position and misplayed the tactics). My score after 5...Be7 remains a healthy 100% - in many games black has gone in for exactly this sort of position and, whether white has had an objective edge or not, in practice it is easier to play white.
A recent game deviated from the above with the also commonly-called-equal 11...Re8 (trying to avoid the weakness on d6 that ...c6 entails) 12.c3 Rb8 (intending Be6) 13.Be3 a6 14.Ba7!? (objectively the position is now dead equal I reckon... but white gets a nicely-anchored Q in the moddle of the board, a tiny spacial edge... and at U2200 level, that can be enough) Ra8 15.Bd4 c6 16.Bb3 Bxd4 17.Qxd4 Be6 18.Bc2!? d5 19.e5 Qg5 20.f4! and I won within another 10 moves - admittedly my opponent went wrong in time trouble, but even in a simple, level position, white's position quickly becomes very strong on even one inaccuracy. 18...Qc7! should be preferred, with at least equal chances, but even here white has scope to play for the win.
If IMs and GMs will trot this line out for black in serious competition, then I will be playing the Belgrade for a long, long time to come. Until people are willing to learn 5.Nxe4 (or maybe 5...Nb4, which I think is a serious try for black), then the BG provides a solid platform to play from.
As for Empty's comments on the 12.Qc4+ line, I am no theoretical expert so I cannot comment on this line. However, I can read, and intrigued by his computer-assisted chagrin, I plugged the line as far as 15...Nf6 into Rybka 3. It gives -0.7, which is no more an edge than white seems to get in several openings which then suddenly disappears on correct play. I do not have 100% faith in the line myself, and so not know how white is supposed to continue after 16.Bc4, but the computer seems to see plenty of compensation and, as a human using his eyes and instincts, a boxed-in Ra8, Kb8 being lined up by the Bf4 and major pieces on the d-file seem to show even there that white has come comp. Indeed, after 16.Bc4 Qd7, 17.Rhe1 might be stronger than 17.Bb5, when Rybka seems to only be suggesting the black queen dancing around d8, c7, c6 or b6...
As for the use of the "!" - we all know in any gambits that the literature is prone to excesses of these marks, and any person with knowledge of opening works such as on the BDG will know that a healthy excess of "!"s is fully permitted, especially on moves you find yourself. Empty's behaviour, as others have already stated, is not acceptable on a forum where many of the contributors have forged friendships, or at least mutual respect for each other, over the years. As for the "mental masturbation" on the thread, as already alluded to by Markovich, any serious attempt to trawl through all the analysis posted, especially the debate between Bruce and our own TopNotch over a critical position, will both be rewarding in terms of opening and general chess understanding. And it certainly holds up to computer analysis as well, though I wonder how useful Empty's computer-assistance proclamations would be if confronted by some of these lines OTB.
Wait... I'm beginning to sound like Lev...