The project I'm using this on is unfortunetly stuck on SL2 for a little bit longer so I won't be going SL3 for a little while, but I'm keen to upgrade as their are some very interesting features in SL3 I'm keen to use.
The Bing Maps Silverlight control is indeed CTP, so feel free to use it for Proof of concepts, pilot applications, demos as much as you like. Microsoft is keen for feedback and want to build the best web based mapping platform the world has ever seen. They
have some very smart guys working on this and I can't wait to see what they do for the release.
The underlying services - Bing Maps Web Service - is production ready and can be licensed for pretty much every scenario you can think of. It is not free however, you can use their staging server for 90 days while you work out your licensing arrangement.
It works out very good for intranet applications where you license per user or tracking apps where you license per tracked asset.
My ultimate goal here is to share as much of the work I do and encourage others to do the same. The DeepEarth map control will become a slim multi-purpose open source control with less restrictions, but our main focus is on providing additional controls
to work with both this map and the Microsoft Bing Maps Control.