when brk was moving along briskly some months ago it had many days when it acted inversely to the dow, like bonds often do. it seemed investors looked upon brk as a haven from the market. now brk may be moving inversely to the market again, which would be a very good sign.
In a working paper that I am working on, I found out that during the years that S&P500 took a dive south, BRK outperfomed it by a 27.7% margins, while during the whole period under study, we outperformed the index only by a 12% margin. During those years that S&P500 returned between 0 to 12.9% (which I termed normal years), we outperformed the market only 11%, and, surprisingly, during good years (ie when the broad index returned more than 12.9%), we only outperfomed it by 6%.
So, as you can see, we actually do better (relatively speaking) during stock market plunges!
So, reasonably speaking, this feature should, ceteris paribus, make BRK to be treated like bonds by the market.