There've been times - like 1998 - when Berkshire stock was very much overvalued, and you'd be better off imitating Buffett than buying him. Hell, back then, Buffett thought Berkshire stock was overvalued, and got rid of $20B of it in buying General Re. If Berkshire is selling Berkshire stock, it's probably a good sign that you should be imitating and not buying in.
...however, I don't think now is one of those times.