Yup, simplejson is much faster than the standard json.

  JSON
  3.56521892548
  SimpleJSON 
  0.727998971939
  Protocol Buffer (fast)
  0.38397192955
  Protocol Buffer (standard)
  4.86640501022
  Protocol Buffer (lwpb)             
  0.323328971863
  cPickle    
  0.811990976334