Google's Geo team today on May 4 launched a new "Distance Matrix service," which is a simple and efficient way to obtain the travel distance and time between many locations when you do not need the full route details for any individual pair. The below applications generates a distance matrix for walking from major London railway stations to several London landmarks. Roll your mouse over the matrix cells, or tap a cell, to see the relevant route.
If you need further assistance, you can also discuss this service with fellow Maps API developers in the Maps API forums.
[Source: Google Geo Developers Blog]