Publishing Nintex Workflows gives a “This workflow already exists” error.

If you’re trying to publish a Nintex Workflow and you get a message saying they already exist, yet you don't see them in the UI, just open up SharePoint Designer and delete them in two spots:  1)  The Workflows list, and 2) Under All Files -> Nintex Workflows.

Nintex Workflow stuck in “Starting” state

If you find your Nintex workflow never leaving the "Starting" state, set the value in the Form Library settings:  ‘Require documents to be checked out before they can be edited’, to “No”.  This is a known Nintex bug:  http://connect.nintex.com/forums/thread/29961.aspx