We've written about Mixpanel, an analytics-focused startup whose backers include Y Combinator, Michael Birch, and Max Levchin. The startup, which currently tracks over 1 billion actions per month, allows developers to track a variety of user actions, including the number of pages a user has viewed, iPhone app analytics , interactions on Facebook apps and email analytics. Today, the company is announcing a UI makeover, and revealing that data volume is growing by 40 percent each month. Mixpanel is tracking how many comments, subscribers, likes, shares, and page views users are getting. And Mixpanel places all of this data on an easy-to-read dashboard for users to check and monitor. Mixpanel has also added the ability for users to create custom email digests of data, that will send daily or hourly emails to users to track certain analytics.