This question has been put to me a couple of times so I thought I'd share my findings. It's not that uncommon a scenario; perhaps you want users to be able to submit a partially completed form or perhaps there are multiple roles involved in the completion of the form and once I've done my but I submit it for someone else to continue. The problem is, InfoPath wont let you submit the form with validation errors (eg blank fields). What can you do?
An elegant variation on the above is to employ the concept of user roles to check whether a particular validation rule should apply. You create a node in your data source for the current user's role and check that node in the data validation for each field to determine whether or not a particular rule should apply to this role. (eg something like: [field1 is blank] AND [userRole is equal to "employee"])