Any one here know anything about this? What's involved in building an online gift registry? I'm guessing you'd use a database to store all your info (server side more than likely). Has anyone here tried to build one?

it definitely would be server side. you can use php/jsp along with jsp to create one. It's similar to creating an online store, like amazon.com for example. First you just need tables like users, wishlists and stuff, and then you can add more features like comments and tracker (item shipping tracker) if you want to.