I’ve held my tongue for the longest time about the demise of a simple Strunk & White grammatical rule: do not end sentences with a preposition. I’ve held my tongue because, as a student of the English language, I recognize that language — and its rules — evolve over time. Spelling changes. Syntax changes. New words develop to replace outdated ones. Once powerful nouns and adjectives are now meaningless (luxury and deluxe, for instance).
But let’s face it. The evolution of language does not excuse laziness, nor does it excuse sycophantic attachments to perishable colloquial norms. When you say, “Where you at?” you have not improved on the language, you have simply institutionalized a grating and lazy convention. “Where are you?” is a far more efficient construct, not only because it uses a verb and verbs are good, but because it is gramatically correct without requiring you to do any extra work.
“Where you at?” suggests that “Where you to?” is right around the corner. Think about that the next time you open your mouth.