I think when you play f4, your king on g1 becomes a little exposed on the a7-g1 diagonal. It can come under fire possibly in some tactics later in the game. That is why it is moved to a safer square h1. It might also allow g4 followed by Bf3 Rg1 for a king side attack. Note that white can afford this as he has a significant space advantage in the center and all his pieces are centrally placed.
Why 11th move kh1 is played in the game betn Anand & Kaspor?

Great answer, SagarJha.
ninadbe, the question should be: Why did Anand smile so long after Kasparov's 19th move? I was watching this game in person, and K left almost immediately after making his move. The crowd turned to the commentators (King and Ashely) who were discussing the game, but I was watching the players, since this was my first WCC game in person. K was barely out the door when Anand brought both his hands up to his face to cover his mouth, which had broken out in a broad grin. I was staring at him, particularly in the close-up moniters, and it took him about 5 minutes to compose himself enough to remove his hands. What did he see that caused him to smile so much in that position? Everybody was saying draw, but I kept telling them he smiled and had to have a reason for it. I got a few weird looks from some people after Anand won.

For an extra little add-on: After this game, the press elevator broke down, so some members from the press room had to ride the public elevators. I had just gotten into a car, which was pretty well packed full, when this huge guy held the door open (I'm 6' 2" and he towered over me). In walked Miguel Najdorf and I had to back up a little to let him in. The two got in and Najdorf said to his companion, "I must tell Garry to take better care of my variation." I came very close to saying, "Who are you to think that the Najdorf Variation is named after you" when I realized who I was talking to and how stupid that would sound. But I opened my mouth, Najdorf looked at me, and so I had to say something, so I said, "Grandmaster, it's an honor to meet you. I always loved the Zurich tournament; you really raised some hell there." "Ah, not enough hell," he replied, and began talking to his companion in Polish.
In this game between Viswanathan and Garry Kasporov why Anand played 11th move kh1. I have seen in most of the games they move king to the corner. What is logic behind this move ?