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This line is covered in "Dangerous weapons" with playing Nf3 - Therefore I am not sure if there is an advantage, but maybe its dangerous 

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Lets quote myself 
there is no "?" but Ward doesnt recommend it for Black - a3, b4 as mentioned by MNb in Ionov,S (2360) - Hlusevich,S (2375)

Thanks, that Wards game was a good one to begin with. There are a few other questions; fortunately I have been able to answer a few myself.

Ward,C (2509) - Hinks Edwards,T (2291) [E30]
BCF-chT 9900 (4NCL) England (7), 25.03.2000
1.d4 Pf6 2.c4 e6 3.Pc3 Lb4 4.Lg5 h6 5.Lh4 c5 6.d5 b5 7.dxe6 fxe6 8.cxb5 d5 9.e3 0-0 10.Ld3 Lb7 11.Pge2 Pbd7 12.0-0 De8 13.Lg3 e5 14.a3 La5 15.Db1 Lb6 16.b4 c4 17.Lg6 De7 18.Td1 Tfd8 19.a4 Pf8 20.a5 Lc7 21.Lf5 Tab8 22.Db2 Ph5 23.b6 Pxg3 24.hxg3 axb6 25.a6 La8 26.a7 Tb7 27.Pxd5 Df7 28.Le4 Ld6 29.Pdc3 b5 30.Ta6 1-0

1. As the plan to advance the a- and b-pawns looks very strong it is logical to play 15...Qe7 (iso 15...Bb6). White remains a little better after 16.Bg6 Rfd8 (d4 17.b4) 17.Rd1 Nf8 18.Bc2 as White still threatens 19.b4.
2. Maybe Black can save a tempo? 12...Qe7 transposes to a game won as Black by Winants, which is further pretty irrelevant (the game I mean). 13.Nf4 Ne5 14.Ng6 Nxg6 15.Bxg6 Rad8 (Qd6 16.Bxf6) 16.Qa4 and again I prefer White, who can play for e3-e4.

So I looked in a golden oldie - a 35 years old treatise of the Indian gamesl written by Pachman and reworked by BH Wood. And here I found an even older recommendation of Kortsjnoj:

Cooper,J (2315) - Plaskett,J (2410) [E30]
BCFch Ayr (4), 10.08.1978
1.d4 Pf6 2.c4 e6 3.Pc3 Lb4 4.Lg5 h6 5.Lh4 c5 6.d5 b5 7.dxe6 fxe6 8.cxb5 d5 9.e3 0-0 10.Ld3 d4 11.exd4 cxd4 12.a3 La5 13.b4 dxc3 14.bxa5 Lb7 15.Pe2 Lxg2 16.Tg1 Lf3 17.Lc2 Pbd7 18.Dd6 Pe5 19.Td1 Dxd6 20.Txd6 Lxe2 21.Kxe2 Pf3 22.Kxf3 Pe8+ 23.Ke2 Pxd6 24.Ld3 e5 25.Le7 e4 26.Lb1 Pxb5 27.Lxf8 Kxf8 28.Lxe4 Te8 29.f3 Pxa3 30.Tg6 Tc8 31.Kd1 Pc4 32.a6 Pe3+ 33.Kc1 Td8 34.Tg1 c2 35.Lxc2 Tc8 36.Kd2 Pxc2 37.Tc1 Ke7 38.Txc2 Txc2+ 39.Kxc2 Kd6 0-1

The first time 10...d4 was used in Spassky-Unzicker, Bath 1973, an eventless draw after 15.Nf3. Critical seems to be

Ionov,S (2360) - Hlusevich,S (2375) [E30]
SSSR-OT56 Uzjgorod, 1988
1.d4 Pf6 2.c4 e6 3.Pc3 Lb4 4.Lg5 h6 5.Lh4 c5 6.d5 b5 7.dxe6 fxe6 8.cxb5 d5 9.e3 0-0 10.Ld3 d4 11.exd4 cxd4 12.a3 La5 13.b4 dxc3 14.bxa5 Lb7 15.Pe2 Lxg2 16.Tg1 Lf3 17.Tg3 Lxe2 18.Dxe2 Pbd7 19.Dxe6+ Kh8 20.Df5 Tf7 21.Kf1 Dxa5 22.Te1 Da4 23.Dg6 Taf8 24.Lxf6 Pxf6 25.Tf3 Dh4 26.Kg2 Dd4 27.Tee3 Dd5 28.Kg1 Kg8 29.a4 Tc7 30.Txf6 Txf6 31.Te8+ Tf8 32.Dh7+ Kf7 33.Lg6+ Kf6 34.Txf8+ 1-0

But I would not dare to conclude based on this game only that White can prove an advantage. 23...Qb3 14.Bxf6 Nxf6 25.Rf3 Tc8 looks very unclear to me.

Finally the notes 1 and 2 above made me wonder if 4...h6 is necessary.
3. 4...c5 5.d5 b5 6.dxe6 fxe6 7.cxb5 d5 8.e3 0-0 9.Bd3 Bbd7 (again d4!?) 10.Nge2 Nbd7 but after 11.a3 Ba5 12.b4 cxb4 13.axb4 Bxb4 14.Bxh7+ it is clear that Black indeed needs to throw ...h6 in between.

MNb wrote on 06/27/08 at 20:52:13:

There is an interesting game analysed in "Starting out: The Nimzo-Indian" (Chris Ward): 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.Bg5 h6 5.Bh4 c5 6.d5 b5!? 7.de6 fe6 8.cb5 d5 9.e3 0-0 10.Bd3 Bb7 (10...a6!?) 11.Nge2 ... just stop here ... - Ward(!) - Hinks-Edwards, 2000, 1-0

Of course Black can count on some activity - but I really think the bishop would be better on d6 (as in the Blumenfeld). Furthermore Whites (extra) pawn on b5 also functions in hindering Blacks play and also may give tactical chances for White.

MNb wrote on 06/27/08 at 02:24:20:

Not so sure - the bishop on b4 may be misplaced compared to the Blumenfeld. If White knows what to do he may be a pawn up with only some compensation for Black - and if you play this line with White your probably know it well. 

I think the aggressive approaches from Black - the "Blumenfeld"-way as mentioned by MNb and the system with a quick h6, g5, Ne4 - can end in a coiled spring position where Black seemingly makes progress with aggressive play but then is pushed back and left with a lot of holes and strategical weaknesses - somehow it reminds me of a Reti-idea.

Against the closed varations (as Markovich mentions) I think Black has to be carefull that the game after exchanging the bishop on c3 is not opened for the White bishop pair - meanwhile White can improve on the kingside.

Personally I dont see the use of the knight on g3, it only clears the way for the queen. I think the position for white is much better if the knights get exchanged even at the cost of the c3-pawn. If black doesnt take at c3, the knight is just in the way.

Matemax wrote on 06/22/08 at 09:02:12:

I dont play this particular line of the Leningrad as black, but the d6-pawn is weak as well and grabbing that c3-pawn looks tricky with the king still in the center. I must say I dont like this line at all for black, something feels very wrong about taking that d5 pawn.

Here's a relatively recent game in this line and I dont see any clear improvements for black, though 12...Nxc3 looks like the best way:
[Site "Maalot Tarshiha"]
[Date "2008.01.07"]
[White "Moiseenko,Alexander"]
[Black "Khenkin,Igor"]
[Result "1-0"]
1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.Bg5 c5 5.d5 d6 6.e3 exd5 7.cxd5 Nbd7 8.Bd3 Qa5 9.Nge2 Nxd5 10.0-0 Bxc3 11.bxc3 c4 12.Bc2 0-0 13.Bh4 Ne5 14.Qd4 Qc5 15.Rfd1 Nd3 16.Bxd3 cxd3 17.Rxd3 Qxd4 18.Rxd4 Be6 19.e4 Nb6 20.Rxd6 Rac8 21.f3 Nc4 22.Rd4 Na3 23.Rc1 Rfe8 24.Ra4 Nc4 25.Rxa7 b6 26.Nd4 Ra8 27.Rc7 Rec8 28.Nxe6 fxe6 29.Rxc8+ Rxc8 30.Rb1 Ra8 31.Rb4 b5 32.Rxb5 Rxa2 33.Rb1 Rc2 34.Be1 Ne3 35.Bf2 Rxc3 36.h4 h6 37.h5 Rd3 38.Rb8+ Kf7 39.Rb7+ Kf8 40.Rc7 Rb3 41.Kh2 Nf1+ 42.Kh3 Rb5 43.Kh4 Nd2 44.Be1 Nb3 45.Bc3 e5 46.f4 Nd4 47.Bxd4 exd4 48.Rd7 Rb2 49.g3 Rd2 50.Kg4 d3 51.Kf5 Rh2 52.Ke6 Kg8 53.Rxd3 Rxh5 54.e5 Rh3 55.Ke7 h5 56.e6 h4 57.Rd8+ Kh7 58.gxh4 Kg6 59.Rd5 Rxh4 60.f5+ Kh7 61.Kd7 Ra4 62.e7 Ra7+ 63.Ke6  1-0

Matemax wrote on 06/21/08 at 16:58:21:

Well, the line that concerns me from White's point of view is the super-closed one that results from 4...c5 5.d5 and eventually Black exhanges unprovoked on c3, plays ...d6, ...e6, and ...e5.  It's chess all right, but I don't think White has any advantage.