For various reason I have to develop on both Lion and Snow Leopard systems. The latest releases seem to be Xcode 4.0.2 for Snow Leopard and 4.1.1 for Lion.
Are there any issues with developing on both these version? I mean creating a project in one, and continuing on another?
There shouldn't be any problem with the code you write, since it's both in the same language. There also shouldn't be any problem with transferring the .xcodeproj file from lion to snow or snow to lion, it should always open the same.
Btw you want to develop under snow and lion for iOS? Because then, there shouldn't be any problem at all. Both the Xcode's are version 4 and all that is different is that the 4.1/4.1.1 is optimized for Lion, runs much faster.