remove the advanced_optimizations concessions and the advanced_optimizations rake task. Simple will do.

Rakefile

@@ -1,6 +1,6 @@
 require 'rubygems'
 require 'closure-compiler'
-  
+
 desc "Use the Closure Compiler to compress Underscore.js"
 task :build do
   js  = File.open('underscore.js', 'r')
@@ -8,20 +8,3 @@ task :build do
   File.open('underscore-min.js', 'w') {|f| f.write(min) }
 end
 
-task :build_advanced do
-  js  = File.read('underscore.js')
-  # remove wrapping anonymous function as this messes with closure compiler
-  # see
-  # http://groups.google.com/group/closure-compiler-discuss/browse_thread/thread/b59b54c1a0073aa5
-  js.sub!('(function() {', '').chomp!("_.initWrapper();\n})();\n")
-  compiler = Closure::Compiler.new \
-    :compilation_level => 'ADVANCED_OPTIMIZATIONS', 
-    :formatting => 'PRETTY_PRINT'
-  min = compiler.compile(js)
-  File.open('underscore-min2.js', 'w') {|f| f.write(min) }
-  #
-  original_size = js.length
-  minimized_size = min.length
-  puts original_size, minimized_size
-end
-