Relax
When you first install the app, there is a check box to receive an email link with installation instructions for the Mac & PC sync apps. If the check box is checked, doubleTwist uses the email address associated with your Google account to send a link to the desktop apps. There is nothing evil there. It's a convenience thing and you can opt out if you don't like it.
I know this because I am the doubleTwist Co-founder
We've been in business since the early days of Android and would not still be here if we were doing shady stuff. We make money from user upgrades and our business model does not involve selling user data. Typically, when app companies rely on user upgrades they are more honest and upfront with their users. It's the free apps that don't have any obvious business model other than ads that you should be worried about. Like the kind that turn on your phone's GPS without good reason, or unexpectedly get your phone hot while you are doing something basic, like reading an article.