I'm a pretty heavy user of TripAdvisor on vacations. I use it with caution, because of the Rate Your Professor effect. People who bother to plug in their evaluations of hotels and travel destinations are either extremely happy, extremely unhappy, kooks, or are sockpuppets. Still, if a place has a lot of evaluations, you can average out all the responses and find something useful. It pointed us to an excellent BBQ joint, when we drove through the Outer Banks this summer.
Seth Kugel talks about vacationing in the era of TripAdvisor. He admits that it has its uses, but it nostalgic for a pre-TripAdvisor World.
Why have my most exhilarating trips of the last few years been to those rare places TripAdvisor and the rest of the Review-Industrial Complex have not yet documented? There was that week spent in San Juan Teitipac, a little town outside Oaxaca, Mexico, that I chose on the advice of a bus driver. (Still not listed on TripAdvisor as of late December: a marvelous 16th-century church that still packs in worshipers every Sunday.) Or that 40-mile hike along an obscure stretch of Brazilian coastline that I made using nothing more than a Google satellite map. It was my lack of knowledge and planning that forced human interactions, ultimately paying off in cheap beds, free coconuts and indelible memories.