For anyone looking to analyze Marketo data in Tableau, there is now a set of pre-built dashboards provided by Tableau. They provide common reports for you to use or customize. You can just update the data sources in the workbooks to have them refresh with your own data.
All these dashboards are now available on Tableau pre-release site for customer download and testing. Just create a free Tableau account to access the site, and select Marketo Pre-built Dashboards from the left pane. We'd appreciate if you could give them a try, and let us know your feedback through the survey tool on the site.
Product Manager at Tableau