Auto-complete show everything by default I have an field of "User reference" on a content type -- using an auto-complete control. This works but our user list is in the order of 300+ and it's difficult to remember who all should be selected for various tasks.

Auto-complete by default shows a list only once you have entered a single character -- is it possible to have the list show everyone the minute you click the text field???
Mabye you can use the Chosen module : 


Install, enable and configure the Chosen module 
change the widget type of your field to "Select list"
in the field settings screen, check "apply chosen on this field" : 



Now in your content edit form, you should see something like this, where the entire list appears in the dropdown, but where you can also type an autocomplete request :