I found this tool http://sab39.netreach.com/Software/Japitools/JDK-Results/46/ which checks for backwards compatibility between different versions of APIs for Java using javadoc.
Is there an tool equivalent to this one for c#/.net?
Here is an example of a comparison between JDK 1.5 and JDK 6 APIs using this tool: http://www.kaffe.org/~stuart/japi/htmlout/h-jdk15-jdk6