Just updated the fresh-out-the-oven Google Maps. 5.0. Simply Awesome. The 3d images of NYC buildings, tilting, rotating, much smoother zoom operations, and better offline support make it a highly recommended update
Application cache (appcache) is a powerful feature in HTML5. However, it does come with baggage. Many (see links below) advocated ferociously against it due to tricky issues it comes with. For someone who is just testing waters, these issues may throw them off grid. Knowing them before hand helps reduce some unpredictable effects.