Didier Pieroux has sent me this interesting news ! I will simply translate the information he gave me:
"Here is a news that has probably been unnoticed in the .NET world but for sure not in the world criticism systems: http://www.adacore.com/2007/09/10/adacore-first-to-bring-true-net-integration-to-ada/
The interest of this news is not the fact that we can develop in ADA on the .NET stack but that this is now followed and developped by a major actor on the ADA world (contrary to A# that has been developped by a university of the USAF [Note : United States Air Force]). Of course, ADA will not takie some market positions to C# or VB. Of course, ADA won't become more popular because it is available on .NET.
No the main important thing is - in my opinion - that it seem to have a demand of the domain that are traditionnaly ADA-oriented (and so Unix-oriented) to open to the .NET world (and so Microsoft). Until now, I had only seen from these domains a true interest to Java. A good news for the "Microsoftees" world in general 
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Interesting also, thare has been a previous initiative to compile ADA to JVM. Today, this initiative is in a clinical death state. I imagine that if AdaCore do a similar step to .NET, this means they think it will be more successfull than with Java !"
Interesting step indeed ! And do not forget that in the same time Microsoft also do a step in the opposite direction with Silverlight and Linux. Loïc Bar has regrouped many articles speaking of that in this news.