Which is correct subject/verb agreement, none of us is smarter than all of us or none of us are smarter than all of us? I think that none stands for no one, so the verb is should be used. However my colleagues think none is plural, so the verb are is correct.

Something whimsical?

"none" may stand for "no one", but does that make it singular?
To me singular means there is one (single) thing we are talking about.
In fact "no one" (Note the word "no"!) is not the same as "one".
Stated differently, "one" is numerically 1; "no one" is not numerically 1, it is 0 (zero).

Maybe we should think in terms of singular and non-singular rather than singular and plural. Zero is certainly non-singular, I'd say, even though it's not plural. "are" is non-singular. Thinking of it like this, we should say "none of us are ...".

Unfortunately, thinking of it like this, we should also say, "none of it are ...". Or does "none" not stand for "no one" after all? At least not always?

Seriously, the textbook answer is "none ... is ...", but 'everyone' says "none ... are ..." if the word immediately preceding the verb is plural.

(And by the way, your colleagues who think "none" is plural really need to think about this a little more.!)