I am currently using blocks in my UIButton category. However I have come across this error which I cannot solve:
error: /usr/include/objc/objc-class.h:
After xcode 4.6 this breaks again. I just fixed this like this :
cd /usr/include/ sudo ln -s /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.7.sdk/usr/include/objc .
Now it works like a charm