realpolitik, I'm not sure about Davies but Zatara and I were talking about Watson recommending 5. Qg4 as one of the dangerous weapons in his latest French book.
But dangerous for whom? Well, move aside y'all for SniperOnG7's first TN on ChessPublishing!
Whether my assessment found in my first post in this thread is harsh or not is up to you to decide...
1. e4 d6
2. d4 d5
3. Nc3 Bb4
4. e5 c5
5. Qg4 Ne7
6. dxc5 Nbc6
7. Qxg7 Rg8
8. Qxh7 d4
9. a3 Qa5
10. Rb1 dxc3
11. Be3 Bd7! (this move is found in the example game on p69 between Flipper and JEB_Stuart, Playchess 2003).
Now White has three pawns but Black is a piece up, while White's pawns can easily fall. Black has far better development (just look at White's Kingside!) and 11...Bd7 is meant to pronounce this contrast even more.
After looking at the position for a while, I believe the most important element of the position is that White can capture back the piece but not without losing his pawns or letting Black accessing important squares. For example, if 12. axb4, 12...Qa2! is the winning shot. Basically it gains control of the queening square with tempo attack White's Rook. Thus play may continue:
13. Rd1 Nxb4
14. Nf3 (trying to develop) cxb2
15. c3 Rg6! and Black wins
or 14. Bd3 cxb2
15. c3 0-0-0!!
16. cxb4?! (White is losing pretty bad anyway) Bb5! <deflection (or is the term decory??) from b1 square>
17. Bb1 Rxd1+
18. Kxd1 Rd8+
19. Bd2 Qc4! with mate threats on f1 and c1 simultaneously.
or
16. Bb1 Qc4 (or Ba4 if you want to be cool 17. Bd4 Qb3 18. Rd3 Rxd4!! 19. cxd4 (decoyed away from the c-file) Qc4!! again and Black wins)
17. Qe4 (forced in regards to ...Bb5) Qxe4
18. Bxe4 Bc6! (again deflection away from b1 square)
19. Bb1 Rxd1+
20. Kxd1 Rd8+ and Black wins since White lacks immediate reinforcements.
Okay, this is just the background, which is necessary to persuade us that Black's Bishop on b4 is quite immune. Obviously JEB_stuart knew this, allowing him to play 11...Bd7!
Now in Watson's book, White played 12. Nf3 and Black's response of 12...cxb2+ is poor. Firstly, since the Bishop is immune, why spend time on it? Is it not better to continue development in order to maintain the initiative? Secondly, after 12...cxb2+ 13 axb4, suddenly the position has equalized, if not slightly better for White. For, without the wedge on c3, White can play c2-c3 whenever which gives Rb1 support. Thus the situation has now totally reversed. Whereas beforehand Black's Pb2 was strong and White's Rb1 was pathetic, now Pb2 is just a weakling.
Therefore my improvement is very logical: 12...0-0-0!TN As we concluded importantly before, Bb4 is actually very comfortable. Meanwhile, by maintaining a dark-square blockade on c3 and supported by Bb4 and Qa5, White's Rb1 is very isolated. For Black, he remains a solid piece up, has many pawn targets, has connected Rooks, has the initiative, has potential passed pawn on b2 etc etc. You can play around with the position but you will find that Black's superior development and assets give the second player a solid advantage. Consequently from this I conclude that Black has a really good time in the mainline 5. Qg4 variation.
BTW, if you find something good for White or disagree with my analysis, please feel free to absolutely trounce it - it takes two to Tango. Though in this case, a French kiss might be more appropriate.