Gilchrist is a legend wrote on 04/27/12 at 08:33:43:

You can study 6.Bg5 against the Najdorf all your life and you will never finish, but if you rely on books you will always be at least one step behind. Therefore you can take a good (but already existing) book and study the main lines there - this gives you an overview and a good feeling for practise. Then you need your own work (play your games, analyse them, work with an engine) and updates from experts (a grandmaster is a grandmaster - and his view is often worth more than a comp evaluation!). One possibility is to subscribe to chesspublishing.

But for 2012. There are so many lines against 6. Bg5 in the Najdorf now, even compared to 2011.

I wonder how much work it would require to write 1. e4 repertoire, with one volume on Sicilians:

Najdorf: 6. Bg5
Kan: 5. Nc3 with 7. Qg4
Sveshnikov: 9. Nd5 Be7 10. Bxf6 Bxf6 11. c3
Taimanov: 6. Be2
Classical: 6. Bg5
Scheveningen: Keres
Dragon: Yugoslav
Accelerated Dragon: Maróczy Bind
Four Knights: 7. a3

As long as I know, Alexander Khalifman made an excellent 1.e4 repertoire with his "Opening for White according to Anand 1.e4" volumes 1-14. And it took him almost 10 years to accomplish.. 
So what more do you need (except money...to buy it)? 
It's true that the first repertoire books started 2003-2004 and so on..are out of date already, but it is a hell of a try.. 

There are to be Grandmaster Repertoire books on a 1. e4 repertoire in the future. But I think there have not many 1. e4 repertoire books as much as 1. d4 or 1. c4/1. Nf3 since playing 1. e4 is generally sharper and probably requires more learning of theory to attempt to claim an advantage in the opening.

For example, I am unsure exactly how much theory one would have to learn to play 6. Bg5 against the Najdorf in 2012, but I am sure that it would be a very substantial amount. And in addition to 6. Bg5, one needs to learn a line against all of the other Sicilians to try for an opening advantage. And then of course the Spanish, Caro Kann, French, Petroff...

A book on 1. e4 against the Najdorf using 6. Bg5 in 2012 would probably be 300 pages long. Although not a repertoire book, there was a book in the 1990s that covered completely 6. Bg5 Najdorf, and I still remember whilst reading it that it was quite a dense book.

A book against the Spanish playing the main line (then Breyer, Karpov, Keres, Zaitsev, Arkhangelsk, Neo-Arkhangelsk, Chigorin, Open Spanish, Marshall Gambit, Berlin Defence, Schliemann, Steinitz, Classical, etc.) would probably require 400 pages.

Kaufman, Wojo, Marin, Avrukh are all about d4, c4, Nf3.  What is going on here? What happen with 1.e4 players? I want to build a repertoire with 1.e4 with books that are as deep and rich in variants as the ones already mentioned. Are there any books that I can read? Please give me a hand!