Not so sure about the 5-pawns vs kinight endgame, it requires great care.
I have rejected 11...Qa5 due to 12.Nb5 Bc5 13.b4! Bxb4 14.Rb1.
Now 14...Bc5 loses to 15.Qxe4+ Kd8 16.Qxb7 and the Nb5 is protected, while 14...0-0-0 15.Na7+! Qxa7 (15...Kb8 16.Nc6+ bc6 16.a3) 16.Rxb4 is looking absolutely horrible for Black.

i don't see there any concrete analysis micawber and there are a lot of moves that are not discussed , like the move 11...Qa5! ....

Hello ,for first, i am new here. I see that the Jaenisch gambit(or Scliemann) is very risky for black and white...

but the fact is that such lines are not played because they have prety good theoretcal depth ,but because of their surprise value and also their parctical value, i.e. if anyone 
spends 50 hours on the 5...d5 variation will probably have an advantage against an unpreared opponent who faces this variation every once in a blue moon....

so i think that the lines after 9.Nxa7!? are playable for Black as sokolov presents in his fine book. Bu i would like to start a much more concrete discussion on the subject , starting frm the variation which i believe is the best chance for Black for an initiative:
  9.Nxa7!?+ Bd7 10.Bxd7+ Nxd7 11.f4 Qa5! 12.Nb5 (forced!) Bc5 13.Qxe4+ Kd8 which in my opinion is unclear with good chances for Black in over-the-board play....

What do you think?

I agree that Carlsen probably not prepared specifically for playing Jaenisch against Nisipeanu.   If one check the Megabase 2010 dossier for Nisipeanus black repertoire, there are no entries with the Jaenisch. 

On the other hand, the games with Carlsen playing white against Jaenisch (according to the same source) are with 4.d3 so he must have prepared for 4.Nc3 as part of switching whenever that took place.  

It may well be that he then also looked at 9.Nxa7 given that there have been articles recommending it.

/ A

Ps.
9.Nxa7 is also given an exclamation mark in the C60-C99 Spanish pdf of the ChessPublishing 1.e4 e5 section.

9.Nxa7 was discussed in the Forum in NIC Yearbook 88 and then it was recommended for White in an article in NIC Yearbook 92 (11...Qa5 was not however not covered there).

I think Carlsen made an informed choice.  Not sure what makes him prefer 9.f4 though.

/ A

I followed Sokolov's suggestion 11.-Qa5 in a recent corr game, but could not get a satisfactory position :

[Event "BI-2009-F-00002"]
[Site "Lechenicher SchachServer"]
[Date "2010.06.18"]
[Round "?"]
[White "Simmelink, Joop"]
[Black "Schroeder, Christoph"]
[Result "1-0"]
[ECO "C63"]
[WhiteElo "2242"]
[BlackElo "2111"]
[PlyCount "113"]
[EventDate "2010.02.17"]

1. e4 e5 2. Nf3 Nc6 3. Bb5 f5 4. Nc3 fxe4 5. Nxe4 d5 6. Nxe5 dxe4 7. Nxc6 Qg5
8. Qe2 Nf6 9. Nxa7+ Bd7 10. Bxd7+ Nxd7 11. f4 Qa5 12. Nb5 Bc5 13. Qxe4+ Kd8 14.
Qd3 c6 15. Nc3 Kc7 16. Kd1 Rad8 17. Re1 Nf6 18. Qg3 Bd4 19. d3 Qh5+ 20. Qf3
Qxh2 21. f5 Kc8 22. Bf4 Qh4 23. Re6 Qh5 24. Ke2 Rhe8 25. Kd2 Qxf3 26. gxf3 Nh5
27. Bh2 Rxe6 28. fxe6 Re8 29. Re1 Bxc3+ 30. Kxc3 g6 31. d4 Ng7 32. Be5 Nxe6 33.
Kd3 Kd7 34. Rh1 Re7 35. f4 Nd8 36. c4 Nf7 37. Bf6 Re6 38. Bg7 Re7 39. d5 Nd6
40. Bf6 Rf7 41. Be5 Nf5 42. a4 h5 43. a5 cxd5 44. cxd5 h4 45. Kc4 Re7 46. Rh3
g5 47. Rb3 Kc8 48. d6 Rd7 49. Kd5 g4 50. Ke6 Ng7+ 51. Bxg7 Rxg7 52. Rc3+ Kd8
53. f5 g3 54. a6 bxa6 55. f6 Rh7 56. Rf3 Rf7 57. Rb3 1-0

Yesterday in Bazna (Romania), Nisipeanu played the Jaenisch main line against Magnus Carlsen. Magnus played 9.f4 (instead of 9.Nxa7) and drew (commentary by Rogozenco):
http://www.chessbase.com/newsdetail.asp?newsid=6455

If the top guns avoid 9.Nxa7, there must be resources for Black in this line.

Hello folks,
Just registered here, though I play online on another site. 9. Nxa7+ is certainly tough for black to meet. What do you think of this idea? -
9. Nxa7+ Kd8 10. Nxc8 Qxg2 (that white knight isn't going anywhere) 11. Qf1 Qf3. White is up a pawn, but the White King remains in the centre for the time being, the white knight on c8 can't be saved, Black avoids a trade of queens and Black can bring the Q rook into action along the a file.