On the matter of DTB having sold all his BRK (but keeping the ticker :) , LTB and others having sold a good part: Tempting, yes, of course. But: If you are

A) in investing in the longterm-buy-and-hold game
and
B) are not convinced Berkshire's economics did permanently change for the worse

but simply of Jim's opinion that it's growth will slowly asymptotically come down to that of the average S&P firm's: Does it then really make sense to sell because it's fully valued currently?

Let's assume the price goes nowhere for 1-2 years. With profitable operating businesses it then will be again in the lower half of it's typical range of price versus value. So you may buy again.

But what do you do with the proceeds from your sales in the meantime? Ok, Jim spends them for a nice Amp. But otherwise? Will you invest them in a clearly overvalued S&P? Are you a talented stockpicker who knows equally surefire investments which are undervalued (if so: Congrats!). Or will you simply wait and receive some % from bonds during those 1-2 years? And does the latter really matter in the grand scheme of things if you are in for another 20+ years?

So I think
- if you are in for the long-term
- and if you don't need to sell a little from to live for your livelihood
- and if you are not a talented stockpicker (then you should have sold and used your skills for trading long ago already)
- and if you are not convinced the good times for our company are over

if none of those "IF's" do apply that then selling because Berkshire at this moment in time is fully valued does not really make sense, and that any eventually high price and "great selling opportunity" should simply be ignored and met with inaction (or by selling covered calls).