Has anyone tried to deploy the ArcMap add-in for both ArcGIS 10.0 and ArcGIS 10.1? There is a target version parameter in the add-in config XML file that needs to be specified. After upgrading the code to VB MS VisualStudio 2010 and ArcObjects 10.1 it can no longer be used in ArcGIS 10.0. What are your strategies for upgrading your add-ins from ArcGIS 10.0 to 10.1 while maintaining the compatibility with 10.0?
With previous versions of ArcMap (9.x) you needed to compile for the lowest common denominator. For example a COM extension written for 9.2 would install in 9.3 as long as any newly added or depreceated ArcObjects were not used. The service pack also made a difference. An extension written for 9.2 SP4 would not install on a 9.2 SP1 machine. However the reverse would work.
Regarding Add-ins in 10.x, I have not tried to install my 10.0 Add-ins in 10.1. I expect the same behavior though. If you need to deploy in both environments then compile the Add-in on a 10.0 developer machine and it should deploy in 10.1. I would contact Esri if this was not the case as it would be a major problem for many users.
If you want to use 10.1 on your dev machine than see this thread: