Warren Buffett has officially stepped down as CEO of Berkshire Hathaway. In an interview Friday, he insisted nothing would change under new CEO Greg Abel. The market seems skeptical though, with shares dropping over 1% on Abel's first day. The stock is actually down about 7% since the retirement announcement in May while the S&P 500 is up 20%. Greg Abel comes from an operations background rather than stock picking. To add to the uncertainty, investment manager Todd Combs left for JPMorgan last month. That leaves Ted Weschler to manage the portfolio, and his recent picks like Sirius XM haven't performed well. Buffett remains board chair and holds 30% of the voting shares.