We are using Samsung Droid tablets and find that Salesforce drag-and-drop does not work. The two examples are 1. Dragging a Contact to the Calendar. 2. When creating a new Report, dragging a field from the left sidebar to the report.
You can't use Drag and Drop on a mobile device unless it's written in HTML5 and specifically handles that. Salesforce browser edition is not currently optimised for tablet/mobile drag and drop.