I have just loaded the ShareKit files into my project (which worked nicely otherwise), and went to build and run (with no code additions as yet).
I received 11 warnings
I'm using reborn ShareKit, but still get some warnings after adding the shareKit folder to my project. For some reason, when compiling the example project, there are no warnings at all. :(
For anyone that has been having problems with ShareKit with iOS5, Facebook released their own wrapper which is way more compatible because you know, Facebook did it.
https://github.com/facebook/facebook-ios-sdk
This fork (https://github.com/mogeneration/ShareKit) compiles/works perfectly on XCode 4/iPhone 3.2.1 Simulator, it should be good for you, besides is based on the latest oficial version :)
Try reborn ShareKit - supported by a community.