How can I make Plupload in D7 start uploading automatically?
As given in the readme file of this module add following autoupload property to your form element as shown below.

$form['my_element'] = array(
  '#type' =&gt; 'plupload',
  '#title' =&gt; t('Upload files'),
  '#description' =&gt; t('This multi-upload widget uses Plupload library.'),
  '#autoupload' =&gt; TRUE,
);


I have tried it and in works fine.