How do you message/email the purchaser an order update? Previously in ubercart 3.x you were able to send messages and log admin notes on each order page. How can this be done using Drupal Commerce? I want to be able to message the purchaser in the order invoice page and also add internal notes if necessary. Which module(s) would I need to achieve this? Can you provide a screenshot of it in action?
Since Drupal Commerce is based on the Rules module, you can simple create a custom rule which watches order status and react when one is changed.

Assuming you have Rules UI enabled you can go to: admin/config/workflow/rules/reaction/import

Here is a simple Rule which you can import:

{"rules_admin_order_update" : {
    "LABEL" : "Admin order update",
    "PLUGIN" : "reaction rule",
    "OWNER" : "rules",
    "REQUIRES" : [ "rules", "entity" ],
    "ON" : { "commerce_order_update" : [] },
    "IF" : [
      { "NOT data_is" : {
          "data" : [ "commerce-order:status" ],
          "value" : [ "commerce-order-unchanged:status" ]
        }
      }
    ],
    "DO" : [
      { "mail" : {
          "to" : "admin@domain.dk",
          "subject" : "Update",
          "message" : "The order changed to [commerce-order:status-title]."
        }
      }
    ]
  }
}


You can then change the add more info, change parameters etc.

Hope this can get you going. :)