My own living point of view is as follows. I base this on what i hear about tableau and what i know about qlik.
Tableau is an intuitive visualization tool that complements an existing data asset (singular) or a data asset that the user controls (like a spreadsheet). Tricky issues are dealing with SQL and query performance and being largely dependent on putting your data together outside the tool. It focuses on visualization, ease of use and it does it well.
QlikView applies an analytic engine to the same need and ends up offering more slice/dice/drill capability for more analysis , root cause inspection to an end user / consumer. The engine and data model can support the users 'next question'.
QlikView also does data integration/combination. So it also solves the business problem of providing an automated way to integrate data and get rid of repetitive data integration tasks. Sometimes it can replace the need for a data mart or warehouse. This capability is a developer skill set and is more than what many business users would want to get into. QlikView applications are therefore authored by a smaller group of users within an organization than a tableau dashboard although the ultimate user consumption of the finished dashboard will be the same or greater than the tableau equivalent. A heavy handed way of categorizing the two is that in qlikview 'we build / you consume' vs tableau 'do it yourself'. QlikView can be used to do most and sometimes all BI needs for an organization. Tableau enhances excel on everyone's desktop by focusing on visualization.
There are other benefits but they are often misunderstood and cause disagreement.
