ReactiveCocoa 2.0 needs to include it's own version of libextobjc specifically. Until ReactiveCocoa 2.0 is properly released, you'll need to specify `pod "ReactiveCocoa", :head` in your project's Podfile.

ReactiveCocoa.podspec

Pod::Spec.new do |s|
  s.name         = "ReactiveCocoa"
  s.version      = "2.0-development"
  s.summary      = "A framework for composing and transforming sequences of values."
  s.homepage     = "https://github.com/blog/1107-reactivecocoa-is-now-open-source"
  s.author       = { "Josh Abernathy" => "[email protected]" }
  s.source       = { :git => "https://github.com/ReactiveCocoa/ReactiveCocoa.git", :branch => "fishhook-off-device" }
  s.license      = 'Simplified BSD License'
  s.description  = "ReactiveCocoa offers:\n"                                                               \
                   "1. The ability to compose operations on future data.\n"                                \
                   "2. An approach to minimizing state and mutability.\n"                                  \
                   "3. A declarative way to define behaviors and the relationships between properties.\n"  \
                   "4. A unified, high-level interface for asynchronous operations.\n"                     \
                   "5. A lovely API on top of KVO."

  s.requires_arc = true
  s.ios.deployment_target = '5.0'
  s.osx.deployment_target = '10.7'
  s.compiler_flags = '-DOS_OBJECT_USE_OBJC=0'
  
  s.subspec 'no-arc' do |sp|
    sp.source_files = 'ReactiveCocoaFramework/ReactiveCocoa/RACObjCRuntime.{h,m}'
    sp.requires_arc = false
  end

  s.subspec 'Core' do |sp|
    sp.dependency 'ReactiveCocoa/no-arc'
    sp.source_files = 'ReactiveCocoaFramework/ReactiveCocoa/**/*.{h,m}', 'external/fishhook/*.{h,c}'
    sp.exclude_files = 'ReactiveCocoaFramework/ReactiveCocoa/RACObjCRuntime.{h,m}'
    sp.ios.exclude_files = '**/*{AppKit,NSControl,NSText}*'
    sp.osx.exclude_files = '**/*{UIActionSheet,UIAlertView,UIBarButtonItem,UIButton,UIControl,UIDatePicker,UIGestureRecognizer,UISegmentedControl,UISlider,UIStepper,UISwitch,UIText,UITableView}*'
    
    sp.pre_install do |pod, _|
      pod.source_files.each { |source|
        contents = source.read
        if contents.gsub!(%r{\"(EXT\w+|metamacros)\.h}, '"ReactiveCocoa/\1.h')
          File.open(source, 'w') { |file| file.puts(contents) }
        end
      }
    end
  end

  s.subspec 'RACExtensions' do |sp|
    sp.source_files = 'RACExtensions/*.{h,m}'
    sp.dependency 'ReactiveCocoa/Core'
  end
end

By the way, I have a fork of this gist with the above changes at https://gist.github.com/brynbellomy/6060338 ... probably better to update this gist, though, and I'll delete mine.

Fixed a couple of things in my fork, works (for me!) now. Usage (in Podfile):

pod 'ReactiveCocoa', :podspec => 'https://gist.github.com/claybridges/6061314/raw/6ffd3b154154af10ccb2134d9a9e7124e78cc746/ReactiveCocoa.podspec'

@brynbellomy: I saw yours, but it wasn't clear how you were getting the 2.0 stuff (versus 1.9.x). Also, the header file spec was missing (and so "ReactiveCocoa.h" wasn't getting found).