OMAHA, Neb. ( TheStreet) -- Berkshire Hathaway ( BRK.B) operating subsidiary NetJets has been on a shaky flight path, but Berkshire's own stock continued to climb ever-higher last week, forcing investors to ask when the climb up by the Warren Buffett investment company would hit resistance. Berkshire Hathaway ran into that resistance this week, as the unexpectedly high initial jobless claims on Thursday, and the continuing economic woes in the Euro nations led by Greece and Spain, pushed all equities down. Thursday was a bad news day for Berkshire, in particular. Berkshire Hathaway lost its last AAA credit rating on Thursday, and also revealed in an SEC filing that its operating subsidiaries had shed another 3,000 jobs in December. Still, last week was a watershed week for Berkshire Hathaway, with Standard & Poor's finally ending the rampant speculation about Berkshire being added to the S&P 500 Index, confirming that the historic marriage of the U.S. flagship equity index and U.S. flagship capitalist would indeed occur. Berkshire Hathaway has set new 52-week high share prices in its B shares four times in the past two weeks. The first time, the new trading high in the Berkshire Hathaway B shares was attained on Jan. 21, when Berkshire shares finally eclipsed the $70 mark, finishing Jan. 21 at $72.72. The first 52-week high was triggered by the 50-to-1 stock split in Berkshire's B shares, a move made to help finance the upcoming acquisition of Burlington Northern ( BNI). The 52-week high was no small feat, even for can-do-no-wrong-in-the-eyes-of-the-market Warren Buffett.