Check a site's privacy score at PrivacyChoice and the site will show you whether your personal data is shared, if the site retains your data after you cancel your account, and more. You can also see if you are being tracked on the site by ad tracking services.
The site currently has released data on 2,500 sites (4,000 sites are scored so far), including Wikipedia (comfort), Google (caution), and MSN (concern). You might be surprised to learn Facebook scores a "comfort" 94 out of 100, although individual Facebook apps may be a whole different story.
The Chrome browser extension shows privacy ratings as you visit sites, alerts you before you share any possibly sensitive data, and keeps you up to date when privacy policies change.
Basically, anyone who cares about their privacy online should check out PrivacyChoice.
[via Ars Technica]