Great idea! Let's assume Google is not evil and would stick to this setting you do. I would feel much better. The option that everybody could download the collected data about him/her would be also nice feature for the hobby data miner. So, Google-guys when will we see GDP in Google Labs?
GDP would allow me to review all of the information that Google retains on me across all services, from all devices, and from all sources. GDP would allow me to determine the maximum data retention period for each of my services. GDP would allow me to selectively opt out of cross-service data mining & correlation, even if it reduced the quality of the services I receive. GDP would allow me to correct any inaccurate data in my profile. And GDP would log and alert me when my data was queried by other services.