Pandora is a well-known site dedicated to what they're calling the "Music Genome Project", where you votes in favor (or disfavor) for specific songs specify your particular taste in music based on the technical differences between songs. Jinni is now trying to categorize movies in the same way as Pandora, with votes counting towards movies and television shows, instead of music.
Without registration, the site operates very similarly to the premier movie database, IMDb. If you look up a movie, you'll get all the information about the actors and plot of the movie all in one place. But Jinni tries to one-up IMDb by offering a host of other categorizations not found on the internet's most popular database, such as "Mood", "Attitude", "Place", "Time Period", and "Based On" (indicating if the movie was derived from a previous work).
If you register, however, you'll see that Jinni uses your opinions to make simple but accurate recommendations for movies that you may have not seen before. In my brief trial of the site, I found that many of the recommended movies are ones that I'd seen before, but were very accurate to my tastes. Take into account that I tend to watch an awful lot of movies, though. Most people would probably find these suggestions very helpful. Jinni also allows you to connect using your Netflix account, which makes setting up your recommendations that much easier.
While not entirely distinguishable from IMDb at first glance, Jinni gives users real value when they register for the site. If you want to know simple facts about a movie, just Google it and you'll likely wind up with the IMDb fact sheet. If you want to delve a little deeper into the nuances of a movie's setting and the tone behind it, as well as get excellent recommendations on movies you might like, use Jinni.