Although i do not make as much money as Buffett does, and i probably reach half the intelligence of the average ETer, i will try to make a posting that makes sense.
I tried to analyze the result but not on a yearly basis. Buffett invests for the long term, so results should be analyze accordingly. I took 5 and 10 year blocks to calculate the average compounded rate for a block to see how things went block by block instead of year by year.
I took the figures from Berkshire as they where published by themselves and putted them in block A. Then i made 10 year periods in block B and calculated the compounded rate for each 10 year period. In block C i did the same but for 5 year periods.
From 1999 on things went wrong:
in the 10 year block the compounded rate went from 28.96% to 6.44%, so down 77.76%.
in the 5 year block the compounded rate went from 33.70% to 5.97%, and 6.91% so down roughly 80%.
In 5 and 10 year blocks you filter out the noise and get a much better view on the results because Buffett is a LT investor.
The fact that for 10 years now things go wrong, proofs that there are at least doubts that Berkshire will stay at a compounded rate of 20.30%. He will have to improve his performance to over 400% of the average performance of the last 10 years.