As previously mentioned on this blog (here & here), Sparrow is a nice interface for using a Gmail or Google Apps email account. It still is a great email client, even though Google bought the Sparrow team, it's just disappointing to know the direction they were headed with an independent app will be swallowed up inside the Google machine.
It's ironic that most of Sparrow's customers will be notified of this through their app. An app they purchased in part because they didn't like Google's iOS interface or Apple's Mail.app.
The good news is that Sparrow for iPhone will continue to work as advertised when it was purchased. And whatever new features the Sparrow team were hoping to add in will hopefully be rolled into a new native iOS email app from Google.