Speech in every language is replete with locutions that are, sensu stricto, ungrammatical or illogical but are tolerated under the colors of current usage (L usus loquendi). Into this category falls the adverb literally, used promiscuously as an emphatic in English (similarly abused by its equivalents in most other European languages). A more recent and widespread case sanctioned by usage is the emphatic absolutely.
Usage can countermand grammar to the point of becoming normative. For instance, no ordinary speaker of English would countenance “It is I” as the non-jocular answer to the question “Who is it?” Even the grammatically correct “Whom did you see?” is rarely to be heard instead of the (originally colloquial) construction “Who did you see?”
The membrane separating usage and catachresis appears to be increasingly permeable in English. All the same, certain cases can only be considered ungrammatical, no matter how common. The frequently heard construction “between you and I” (in British as well as American English) falls into this category and is to be censured accordingly.