We are therefore happy to introduce a new service to the Maps API family that enables applications to determine elevation profiles. Using either the new ElevationService Maps API v3 class or the Elevation Web Service you can request the elevation in meters for one or more sets of coordinates, or you can request a specific number of elevation samples equally spaced along a path. If any sampling points are over bodies of water, the service will return the depth relative to sea level as a negative number.
They also have a nifty interactive map where you can add points along a route and see an interactive graph of the elevation changes. I tried it out on my treks across the Grand Canyon and Uluru in Australia. Very slick, and really useful for those getting biking or running directions.
Google Geo Developers Blog: Ain't No Mountain High Enough...