You can switchback to one column in the 'more' menu.
>> "How do you read this, particularly in three-column mode, and be reasonably sure not to miss a post?"
I think that might be your problem. Maybe Google doesn't think many people want to see every post in their stream. Personally I just skim through it and see what catches my eye. I much prefer this design (2 column, my 15" monitor apparently isn't large enough for three regardless of the lagre whitespace to either side of the two columns).
>> "How do you read this, particularly in three-column mode, and be reasonably sure not to miss a post?"
I think that might be your problem. Maybe Google doesn't think many people want to see every post in their stream. Personally I just skim through it and see what catches my eye. I much prefer this design (2 column, my 15" monitor apparently isn't large enough for three regardless of the lagre whitespace to either side of the two columns).