What is your money metric - the event that if you see a lot of it happening it means your users are getting more value out of your product.

For example:

• For Twitter, that may be tweeting.
  
• For Expensify, that may be submitting an expense report.
  
• For Toutapp, that may be number of emails sent out through their app.
  

Find the one metric that represents value for the user so you can make sure you are monitoring it closely.