I have several workflows in our environment that support different business processes, and almost all of them require attachments! But i have come to notice that working with attachments on Nintex is quite stressful and very frustrating, and from the articles/discussions I have read so far it seems like its the same story with most developers. And Nintex is not really doing anything to improve on this functionality!
One example of this is the ability to pass attachments from one approver to the next, or carry initiator's attachments to the next approver task without having to implement web-services with complex XML code!
One other common requirement is the ability to remove old attachments and add new one when a task is returned to the originator/initiator to revise!
For scenario 1 above, I have a custom solution of displaying the attachment URLs on the next approvers task (Not using web services!), but scenario 2 is quite complicated!