We're living in the era of retail-tainment, where we've come to expect live music at the Apple Store, mountaineering discussions at REI and product demos at Bed Bath & Beyond. Not surprisingly, well-known talent is stepping into this area because it's a welcoming and unique environment in which to plug one's latest project. Marketers, who benefit greatly from the star power, are only too willing to make this all happen. (Sarah McLachlan recently played a live show in a JetBlue terminal; no word on how many fans watched the concert instead of catching their flights.) Now, soul singer Joss Stone is hitting the Nine West flagship store in midtown Manhattan on Sept. 10 for a live performance. She'll also be at the Macy's on 34th Street in Herald Square that day to chat with fans and sign copies of her new CD. It's part of Fashion's Night Out, an annual charity event in New York, and Stone's promotion of a co-branded line she designed for Nine West. (She even wrote a song about it!) Stone's Vintage America collection includes shoes, clothing, jewelry and other accessories. Everyone involved hopes that grooving while you shop will boost the bottom line. You have to admit, it's catchy.