Re: "To whom"

Yes, but colloquial can be used by certain people as the opposite of any
of those terms. Sometimes it's perjorative (meaning the "bad English"
you hear from less educated people/people who speak other dialects),
sometimes it just means informal English, but either way you can't call
the relativization strategy we've been discussing colloquial! It's
applicable in all registers including formal ones and is far from a
dialect phenomenon. Basically, the word colloquial in any of those
senses is not applicable to leaving prepositions in place in relative
clauses, because it is proper, standard English usable in formal
contexts as well as informal ones.

>
>> Calling it colloquial is a dismissal, dismissing it
>> from"proper"/"formal"/"standard" English!
>
>
> But those aren't synonyms. ><