Jonathan Hawkins from the Atlas/ASP.NET team just posted a nice tutorial walking through how to build a map-based mashup using the Atlas Virtual Earth control and some custom web-services that serve up mountain information (note: Jonathan is an avid hiker!). You can read and download his tutorial here. You can also learn about the great Atlas Mashup Contest here (and win a free XBox 360!).
This tutorial shows off some of the great "client-centric Ajax programming" power available with Atlas. For more on Atlas (and to see my own fun tutorial building a todo task list), check out http://atlas.asp.net. I also posted my slides+demos from an Atlas presentation I did in Amsterdam here.
Hope this helps,