guard-bacon wasn't really working out for me, just run it using guard-shell instead.

Gemfile

@@ -4,7 +4,7 @@ group :development do
   gem "rake"
   gem "bacon"
   gem "guard"
-  gem "guard-bacon"
+  gem "guard-shell"
   gem "rb-fsevent"
   gem "growl"
   gem "mocha-on-bacon"

Gemfile.lock

@@ -5,9 +5,8 @@ GEM
     growl (1.0.3)
     guard (0.8.8)
       thor (~> 0.14.6)
-    guard-bacon (1.0.2)
-      guard (~> 0.8.4)
-      schmurfy-bacon (~> 1.2)
+    guard-shell (0.3.0)
+      guard (>= 0.2.0)
     metaclass (0.0.1)
     mocha (0.10.4)
       metaclass (~> 0.0.1)
@@ -15,9 +14,6 @@ GEM
       mocha (>= 0.9.8)
     rake (0.9.2.2)
     rb-fsevent (0.9.0)
-    schmurfy-bacon (1.2.1)
-      term-ansicolor
-    term-ansicolor (1.0.7)
     thor (0.14.6)
 
 PLATFORMS
@@ -27,7 +23,7 @@ DEPENDENCIES
   bacon
   growl
   guard
-  guard-bacon
+  guard-shell
   mocha-on-bacon
   rake
   rb-fsevent

Guardfile

 # A sample Guardfile
 # More info at https://github.com/guard/guard#readme
 
+def run_spec(s)
+  `bundle exec bacon #{s}`
+end
 
 # parameters:
 #  output     => the formatted to use
 #  backtrace  => number of lines, nil =  everything
-guard 'bacon', :output => "BetterOutput", :backtrace => 4 do
-  watch(%r{^lib/cocoapods/(.+)\.rb$})     { |m| "spec/unit/#{m[1]}_spec.rb" }
-  watch(%r{spec/.+\.rb$})
+guard :shell do
+  watch(%r{^lib/cocoapods/(.+)\.rb$}) { |m| run_spec("spec/unit/#{m[1]}_spec.rb") }
+  watch(%r{spec/.+\.rb$})             { |s| run_spec(s) }
 end