I know "coke" gets used a lot generically when ordering a soda at restaurants, I do it myself. Very occasionally, a Pepsi based franchise will get in trouble for not correcting the customer on this point. However, using it as the generic term in regular conversation isn't something I've seen.
EDIT: @ E. Spaceman (below). I once saw a letter to the editor of Time magazine from a writer in Atlanta claiming that aluminum Pepsi cans weren't recyclable, so that's why you should buy Coke instead. They take this shit seriously.