The hg sources download/re-compilation tutorial is great, but you don't need to do all that.
Just browse to http://sourceforge.net/projects/zbar/files/iPhoneSDK/beta/ and download ZBarSDK-1.3.1.dmg, and everything will work out of the box for the latest architectures (in my case armv7, armv7s).
Update:
Some of you reported issues with ZBarSDK on XCode 5, iOS 7 or architectures arm64... well I went back to this project today and experienced similar issues and found that there is a ZBarSDK library that is compiled to work with iOS 7 at: http://www.nerdvision.net/app-development/ios/zbar-sdk. I Just replaced the old files with the new ones and my project compiled. Note that the Architectures in my project's Build Settings are set to amrv7, arm64 ($ARCHS_STANDARD), Base SDK is set to iOS 8.0 and I have the Build Active Architectures Only flag set to Yes.
There is a question here at SO about this: zbar SDK dont work for armv7s(iPad 4 iOS 7)
Thanks to @cdescours for the tip!