I stumbled on an awesome new feature of Google Maps yesterday: once you've plotted a route for driving directions, if you hover over the route on the map, a little square appears, with the hover help "Drag to change route". Drag the square, and the route dynamically changes to go through the point you are dragging. The list of driving directions update as well, of course, with your dragged point included as a new intermediate milestone.
I showed this to a co-worker, who literally stared slack-jawed as my driving path wiggled all over the screen, and then finally said, "That's impossible!". What he meant was, it's impressive to be able to make server round trips as you drag, with enough responsiveness to serve new route images quickly enough to get that dynamic and fluid feel.
Other stuff: once you have multiple milestones in your driving directions, you can drag and drop them to reorder them, and there's an "avoid highways" checkbox to stick to the scenic routes.
The amazing gets amazinger. Funny to discover it by accident, though. Isn't there a blog that announces these things? The Official Google Blog has bigger fish to fry (acquisitions, global warming, privacy concerns). Turns out Google Maps Mania is the place, and had the news about draggable driving directions two weeks ago.