In reality Buffett has made more than 40% since in addition to the intrinsic value of GS warrants (market price of common = $165 in excess of strike price of warrants = $115), the warrants also contain a time value component of value (even when the underlying common stock trades below the strike).
The interesting thing is that Wesco Financial also owns $205 million of these convertible preferreds and this investment is big enough that Charlie breaks out the fair value of it with each 10-Q/10-K (though you have to back out the value of other non-listed equity investments like AXP, JNJ) that WSC owns.
At year end 2008, the fair value of the GS preferreds was listed at $209,510. This means the warrants were given a value of $4.510 million while the underlying GS common was trading at $84.39. Since WSC owns 1.78 million warrants, this means they were given a value of $2.53 per warrant.
At 3/31/2009, using the same methodology the warrants were valued at $32.577 million ($18.30 per warrant) while the underlying GS common was at $106.02.
So it looks like time value which decays over time are probably worth around $20 per warrant now if I just swag it. Add in $50.84 of intrinsic value per warrant as I write this -- and I get an approx. total value per warrant of over $70.80 per warrant.
BRK owns a total of 43.478 million GS warrants for a total market value of around $ 3 billion+. That's more like a 60% return (not including the straight 10% annual dividend return on the preferreds). Not bad for the old man who supposedly lost it when he bought the GS preferreds, eh?
wabuffo