From Pabrai's Interview with Steve Forbes:
Pabrai: You know, when I went to Warren's Berkshire headquarters last year, my friend Guy asked Warren, he said, "Warren, Mohnish has a nap room in his office. Do you have a nap room?" And Warren's answer was, "Yes." OK, so I was surprised. So I said, "Warren, you're telling me in Kiewit Plaza, there's a nap room for you." He says, "Yes." He says, "Not every day, but every once in a while, I need to go to sleep in the afternoon."