We've tried to make it as open as possible - code is available (its open source), we write openly about this at the very start, we have a policy online, made it easy to opt-out. If you have other ideas how to make it even more friendly, more visible, etc - let us know please.
Still, we've preferred so far to keep it opt-out since it's crucial for us to see major product trends (which features are being used more, product growth MoM etc). Opt-in at this stage realistically won't give us this information.