What does js_css_optimizer do well if your here you probably know but basically it

It compress your Javascript and CSS Files to reduce the size this makes a small saving. It also bundles the JavaScript and CSS Files so if you have many files only one call to the server for the js and one for the css this makes a big difference.

The code I used is like this:

page{
  typeNum = 0
  meta.author = Digital Marketechs
############## Google verifier
  meta.google-site-verification = IHdsBN-BCm8bzf4exdJBUf-EYuGpgcj51NASbjT6s00

############# Yahoo verifier <META name="y_key" content="96c2c2bd83aab1a3">
  meta.y_key = 96c2c2bd83aab1a3
  meta.robots = index,follow

  shortcutIcon = fileadmin/templates/images/favicon.ico
  
  includeCSS {
   screenStyle = fileadmin/templates/css/style.css   
   screenStyle2 = fileadmin/templates/css/style4menuRW.css
   screenStyle3 = fileadmin/templates/css/style4menu2RW.css
    screenStyle {
     media = screen
     import = 0
     compress=1
   }
    screenStyle2 {
     media = screen
     import = 0
     compress=1
   }
    screenStyle3 {
     media = screen
     import = 0
     compress=1
    } 
 }
 includeJSlibs{
  jquery = fileadmin/templates/javascript/jquery-1.3.2.min.js
  jquery.forceOnTop = 1
  curvycorners = fileadmin/templates/javascript/curvycorners.js
  rwMenu = fileadmin/templates/javascript/rwMenu.js
  sifr = fileadmin/templates/javascript/sifr.js
  dimensio = fileadmin/templates/javascript/dimensions.js
  bgiframe = fileadmin/templates/javascript/bgiframe.js
  swfobject = fileadmin/templates/javascript/swfobject.js
  gaLib = fileadmin/templates/javascript/ga.js # google analyitics stuff
  
  common={$const.path.scripts}common.js
    common{
      compress=1
   }   
  }
 includeJS {
 file1 = fileadmin/templates/javascript/misc.js
 file1.compress=1
 }
}

I noticed about a 20% speed increase so that was an easy saving.

As Matt Cutts said in his presentation on the state of the index page speed is now an important factor that Google are looking to bring into the ranking algorithm. How to increase page download times in Typo3 starts with the easy stuff like the js and css optimizer.