Google announced they now integrate with Salesforce to produce offline conversion metrics. Google said the new "AdWords Conversion Import for Salesforce measures the value of your offline conversions that result from online AdWords clicks, without the need to reconcile your AdWords and customer relationship management (CRM) data manually."
All you need to do is link your AdWords and Salesforce accounts. Then you set your various "milestones" such as 'lead qualification' or 'deal won." Then when a user clicks your ad and visits your website, your website captures a unique Google click ID that tells your website which ad the visitor clicked on. If that visitor submits a lead form on your website, your website passes along the click ID to Salesforce, where it’s stored with the corresponding lead and any future sales opportunities.
Here is how it works:
Here is a more technical diagram:
To participate, you need to apply over here.