Xintiandi is one of the most popular tourist stops in the city due to highly-stylized reproductions of shikumen houses, once ubiquitous as tenement-style residences and now a reminder of an idealized Shanghai. We say "reminder" only because Xintiandi has more in common with a theme park than the actual shikumen housing arrangements; try Tianzifang (across Chongqing Road and south about five blocks) for a bit more authenticity.
Then again, this pedestrian zone is popular for a reason: some of the best dining and nightlife in Shanghai can be found here. Based both north and south of Xingye Road, this trendy, high-end area appeals to the full range of tastes. Cuisine can be had from Brazilian BBQ to pizza to quality Chinese (Din Tai Fung and Crystal Jade are praised highly), while the gamut of nightlife options is available. G-Plus is your club du jour, good live music can be found at Luna and Cigar Jazz Wine, and you'll find your usual beer and cocktail joints interspersed between. Just be careful with your credit card tab; this area is one of the most expensive in Shanghai (and that's saying a lot).