Assigning a texture to a renderer

Hi

no matter what I try I can't dynamically assign a texture from a file - this should be easy! Can anyone see why my code is not working?

And I'm looping through all renderers just because I figured assign the texture to ANY renderer in the scene - I don't care which one just show me the damn image!

Code assigned to the Canvas object:

 public string url = "http://images.earthcam.com/ec_metros/ourcams/fridays.jpg";
 IEnumerator Start() {

     Debug.Log( gameObject.name + ":: Start");
     WWW www = new WWW(url);
     yield return www;

     Renderer[] allRenderers = GetComponentsInChildren<Renderer>();
     foreach (Renderer thisRenderer in allRenderers) {
         Debug.Log ( gameObject.name + ":: " + thisRenderer.name + ": " + thisRenderer.enabled);
         thisRenderer.material.mainTexture = www.texture;
     }
 }

And by the way when I run this code I get 2 renderers found, both visible in the scene. Neither of them displays the loaded image. I've also tried loading an image from my local hard drive, in case its a cross domain issue (though its not because I can debug the code and browse the www object, an image is definitely loaded)

Please help! If I can't even get this working then I'll have to give up on Unity development and take up kitten juggling...

Ben