Application Cache is- as Jake so infamously described -not a good API. It was specced and shipped before developers had a chance to figure out what they really needed, and so AppCache turned out to be frustrating at best and downright dangerous in some situations. Its over-zealous caching combined with its byzantine cache invalidation ensured it was never going to become a mainstream technology. There are very few use-cases for AppCache, but I think I hit upon one of them. Six years ago, A Book Apart published HTML5 For Web Designers. A year and a half later, I put the book online.