Try out your map mashup by playing in the sandbox. Better yet, easily switch between Google, Yahoo and several other mapping providers.
If you're new to Mapstraction, check out this presentation (embedded below) from last week's Where 2.0 conference. In the slides, Andrew Turner and Evan Henshaw-Plath give an introduction to using Mapstraction, as well as an overview of geo-related data formats.
Of mashups listed in the ProgrammableWeb database, over a third are mapping-related, most of these using Google Maps. If something were to change with the terms of service or features, thousands of developers would be re-writing entire websites.
I'm in the process of writing a map scripting book and am using Mapstraction examples wherever I can. Unless you take advantage of very specialized features of a mapping API, it makes sense to utilize a write-it-once library like Mapstraction. Between the the sandbox and the slides, you should be well on your way.