I have only one game in practice after 6.dxc5 against a much lower-rated opponent than me. During the game i was afraid that i did a wrong choice of the opening. The position indeed looked prospectless! At the end i won the game very easily, without my opponent commiting a major mistake. I was congratulated by my team captain that i had the right attidute (he didn't know that i was writting a book in the Tarrasch!): "Great strategy! You had a position where you cannot lose and when it is clear that you were equal with Black you pressed for the point and your opponent didn't play well to draw!"

The 6.dxc5 chapter took me far more than any else chapter to complete the analysis. During that period Jacob was convinced that we won't find equality for Black. He said that that wasn't a catastrophe, on the contrary our book will offer something new! During that period i played about a dozen of training games with opponents 2250-2350. Every time i reached a great position after the opening even scoring above 50%. When the analysis was over and finally we could claim equaity i wanted to play that position more than any other position on the whole Tarrasch! What happened?

-> I was specialized in that position. Meaning that i was very well prepared and i had become much better experienced than any opponent i played (this doesn't mean that i remebered all my analysis! I am known as a plyer with a bad memory). This gave me a competitive advantage and a great one, as my practice showed. And contrary to what i expected i never got a dead drawn position! Knowing the position well gave me the confidence to deviate a bit from my analysis when i wanted to avoid a dead draw, even knowing that i'll be a bit worse, but knowing that i can play those positions better meant that i actually had a practical edge!

-> I was playing a "safe" position. I had the feeling that i can draw this position any time! What a feeling! As i think we proved in the book, Black is objectively equal or very close to it. 

And last but not least, Black can play the Tarrasch in reply to the English-Reti-Catalan Lines where 6.dxc5! is no longer possible! In fact this was my idea when i started playing the Tarrasch at 2006. I didn't like all those deviations. I stydied only the main lines with 6.g3 back then. After a while i was playing the Tarrasch also against 1.d4 bluffing really but my opponents accepted my bluff and entered the main lines after 6.g3 anyway!

Now, looking this from White's perspective, i can say with confidence that i'll never chose 6.dxc5 in my own games. Instead i'd chose 9.dxc5 Bxc5 10.a3 or 10.Bf4 which is a much more practical choice, with less risk and a more principled (classical) position. 6.dxc5 is really a computer's discovery. Tarrasch Defence is around for 150 years with the greatest minds testing it. Why none of them repsected 6.dxc5? This was a question troubling me for a long time...

As i have said again and again to many people asking me the same questions. Tarrasch cannot satisfy everyone!. If you like piece play, open positions and want to play for the win with Black then it is one of the best openings you can choose. Try it in practice, for example in online blitz games first. Reading theory tells you nothing about the opening and the feeling of playing these kind of (classical) positions. And believe me, the theory of this opening is not great. The exact positions you need to know are limited. Compare it with the Nimzo for example, or the KID or the Grunfeld. And remember that in those openigns you have to know and other lines to counter the English-Reti and so on!

I own the book and read almost half of it so far, including the 6. dxc5! chapters. The final positions do not seem too difficult to play for Black. The endgames seem drawish, but many other openings end with such positions as well in their main lines, such as Slav. The endgame with the isolated e-pawn in the 9. Bd2 chapter and the endgame with the pawn up for White and the Black rook on c2 in 9. Qd2 chapter look quite easy to draw with as Black, and White seems to need accuracy to get to this position. I doubt players facing the Tarrasch would deliberately attempt to get into a drawn endgame, unless the opponent is much lower rated. Still in that case, the lines are more than 20 moves deep, so accuracy is needed.

We all are still awed into silence 

But (half-)seriously: I took the book to Ghana (so at least one of the copies has already been to Africa!) and wanted even to ask at the customs if they could confirm that, but before I could open my mouth, my wife had already given 10 Cedis to the officer (as a "christmas present", of course), who afterwards didn't want to touch our luggage any more 
After acclimatization, I wanted to start studying the Tarrasch, but as the Ghanaens like to say, before that "I had one or two things to do" (the usual excuse in Ghana for arriving late or leaving early or everything else), i.e. one or two other openings to check and similar things (), so I had to confine myself to a few cursory looks  . At least, they confirmed my very positive impression I had got when reading the pdf excerpt some time ago.
When I get into serious business with the book I shall break my silence!

Best regards,

Zwischenzugzwang

Karpov did quite well against the QGD as well, but it does not stop people from playing it still.

Does Karpov write book reviews in the first place though?

It seems, some user are surprised, why I mentioned Karpov?! As a Karpov fan I vividly remember his games against the Tarrasch:
Karpov - Kasparov, 1984:

1.d4 d5 2.c4 e6 3.Nf3 c5 4.cxd5 exd5 5.g3 Nf6 6.Bg2 Be7 7.O-O
O-O 8.Nc3 Nc6 9.Bg5 cxd4 10.Nxd4 h6 11.Be3 Re8 12.Qb3 Na5
13.Qc2 Bg4 14.Nf5 Rc8 15.Bd4 Bc5 16.Bxc5 Rxc5 17.Ne3 Be6
18.Rad1 Qc8 19.Qa4 Rd8 20.Rd3 a6 21.Rfd1 Nc4 22.Nxc4 Rxc4
23.Qa5 Rc5 24.Qb6 Rd7 25.Rd4 Qc7 26.Qxc7 Rdxc7 27.h3 h5 28.a3
g6 29.e3 Kg7 30.Kh2 Rc4 31.Bf3 b5 32.Kg2 R7c5 33.Rxc4 Rxc4
34.Rd4 Kf8 35.Be2 Rxd4 36.exd4 Ke7 37.Na2 Bc8 38.Nb4 Kd6 39.f3
Ng8 40.h4 Nh6 41.Kf2 Nf5 42.Nc2 f6 43.Bd3 g5 44.Bxf5 Bxf5
45.Ne3 Bb1 46.b4 gxh4 47.Ng2 hxg3 48.Kxg3 Ke6 49.Nf4+ Kf5
50.Nxh5 Ke6 51.Nf4+ Kd6 52.Kg4 Bc2 53.Kh5 Bd1 54.Kg6 Ke7
55.Nxd5+ Ke6 56.Nc7+ Kd7 57.Nxa6 Bxf3 58.Kxf6 Kd6 59.Kf5 Kd5
60.Kf4 Bh1 61.Ke3 Kc4 62.Nc5 Bc6 63.Nd3 Bg2 64.Ne5+ Kc3 65.Ng6
Kc4 66.Ne7 Bb7 67.Nf5 Bg2 68.Nd6+ Kb3 69.Nxb5 Ka4 70.Nd6 1-0

Another very good game was Karpov - Illescas Cordoba, 1993

1.c4 c5 2.Nf3 Nf6 3.Nc3 e6 4.g3 Nc6 5.Bg2 d5 6.cxd5 exd5 7.d4
Be7 8.O-O O-O 9.Bg5 cxd4 10.Nxd4 h6 11.Be3 Re8 12.Rc1 Bf8
13.a3 Bg4 14.h3 Be6 15.Nxc6 bxc6 16.Bd4 Bd7 17.Qd3 Nh7 18.Be3
Bd6 19.Rfd1 Be6 20.b4 Nf8 21.Na4 Ng6 22.Qc3 Bd7 23.Nc5 Bxc5
24.Bxc5 Rxe2 25.Be3 Qe7 26.Bf1 Rxe3 27.Qxe3 Qxe3 28.fxe3 Re8
29.Kf2 Ne5 30.Rc5 Re7 31.e4 Be6 32.b5 cxb5 33.exd5 Bd7 34.d6
Re6 35.Bxb5 Rf6+ 36.Kg2 1-0

Okay, these games are not the latest, but it´s obvious, that Karpov has a great feeling for these positions.

If Karpov writes a review, then what if Kasparov writes a review as well?

Until Karpov doesn´t write a review about GM 10 and gives his blessings, I´ll still be sceptical to this defence.

From a strategic point of view i am wondering if there is a better move than 13...d4. Black could play ...f6 is Bb2 comes and play instead for Bf5-Be4. I cannot check this from where i am now, i was just wondering....

This is going to be examined in some depth in a next QC newsletter for sure.