Black shouldn't be too uncomfortable in this position. His King can always move back, and White doesn't have enough pieces out to start a real attack yet.

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But not enough for the lost center pawn.

This ...Nxe4 variation is why Bc4 in the Four Knights is bad, and 4.Nc3? in the Two Knight's Defence leads to this same position.

I have played this before.  It depends on the player, sometimes it can through white a unexpected surprise.  Though I do not recommend this with a high caliber player.

This is what my opening book proposes but white is still left without any advantage.

Interesting post on an interesting opening. I have to admit I had never seen this played before. According to my files I have over 500 instances of the position after 6...d5 with Black scoring around 70% though I never trust just the plain statistics. The center for Black is quite strong and his pieces seem to be easy to develop. There is a game by super GM Novikov where he lost (as White) in 19 moves. Fritz evaluates the position at about +1 for Black

don't think that taking the pawn with your bishop was a good idea, even if you do get his king out of position

Black is slightly better after Bxf7, but there is still alot of chess to play. You should play something besides 4.Nc3, I like 4.d4, but 4.Ng5 or 4.d3 are both good options.

What about Ng3 after d5? 

Black is completely fine

cool