This casually stylish restaurant, whose namesake operates similar establishments in Paris, London, New York, and elsewhere, recently celebrated its sixth anniversary. And it's as popular as ever. No surprise given the smart design, friendly staff, welcoming atmosphere, and moderately priced menu of eclectic dishes prepared by the most consistent kitchen on the Beach. But the single ingredient that's vital to Joe Allen's continued success is this: its location. Hard by Biscayne Bay where the Venetian Causeway links to Miami Beach, Purdy Avenue isn't the forlorn warehouse strip it was when the restaurant opened, but it is still far off the beaten tourist path. That happy fact has allowed Joe Allen to concentrate on nurturing its faithful clientele of local residents. In return, they have adopted the place as a second home. And it's always nice to come home.