With V1.1 of the Framework shipping
I though i'd post a couple of links I have found useful..
DennisAn wrote a great whitepaper on how to target different runtime
versions... https://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetdep/html/sidexsidenet.asp
And if you want to know the details of what is the breaking changes in V1.1
you can check out this list:
This list we generated from beta customers, our own testing and our own "by
design" changes:
https://www.gotdotnet.com/team/changeinfo/Backwards1.0to1.1/default.aspx
Should we have a contest to see if who can find a breaking change not
listed? ;-)
Hope that helps!