I guess is was inevitable that the new players in online mapping would at some point try to address the use of their systems in commercial applications in a more targeted manner, but interestingly Yahoo and Google seem to be going in different directions.

I remember when Google maps was first released with a great user interface and some quick and cartographically pleasing maps. There was no API and all the talk and development effort was targeted at getting access to the same data and maps. Very quickly people worked out how to decode the javascript to get direct access to the map tiles by URL based on Lat/Long My House Google Tile http://kh0.google.com/kh?n=404&v=6&t=tqsrsrsrsrrqtttrsqsq

Many Applications sprung up that allowed direct access to the map tiles, such as google wallpaper which created large mosaics you could download and print out. I wrote an extension for ArcMap that streamed the tiles in as a background layer. however google soon released an official javascript API, and started to ask people to take their sites down. When the API was released most people started using this for building sites.

It seems now that google are offering commercial licenses for any business use of the API rather than just restricting it in the terms and conditions. For prices starting at 10K per year you can do anything with the API for internal or external sites for commercial uses. There are no technical limits on the type of application you can build as long as you pay or do it non commercially. Currently this only available in the U.S.
Yahoo on the other hand are making their API free for commercial use, but placing some fairly serious technical restrictions on what you can do with the API. The main issues seem to be limiting its use for tracking and real time applications such as GPS locating or vehicle and fleet management, which is interesting as it implies this might either be an area that yahoo want to get into, or more likely risks taking revenue away from their data provider Navteq who make a lot of money from "traditional" companies working in this area.

Usually Google are the ones to do it for free, when everyone else charges for a service so its interesting to see that they have followed the same path as Microsoft and ESRI and decided to charge for commercial services alongside free public ones rather than limit what you can do with them where as Yahoo are going the other way. I guess its actually easier for Google to engage in a commercial relationship, than to try and police usage of their system, as Yahoo will have to do.

Google have also added a click limited Geocoding service to their API, although again not covering the UK.