Tabletop.js is a fantastic, open-source JavaScript library that lets developers easily integrate data from Google Spreadsheets into their online projects. I've used it, even contributed a minor feature, and love it for prototyping. Non-programmers love being able to update a project via Google Spreadsheets' hyper-intuitive interface.
That said, I'm extraordinarily wary of using Tabletop in production. Instead, at the Wall Street Journal, we use a bit of middleware to "prune" our Google Spreadsheets-based data and then cache it on our own servers. A few brief reasons: