Google, perhaps reacting to criticism that it's keeping a whole load of your data in disparate places, has launched a "dashboard" that displays all the info that the search giant is keeping on you, and allowing you to modify that data.
The service, which can be found at google.com/dashboard, covers your account, alerts, Blogger, calendar, contacts, custom search engines, docs, finance, friend connect, Gmail, iGoogle, health, Latitude, mobile sync, Orkut, Picasa, your public profile, reader, shopping list, talk, tasks, voice, web history, and YouTube. There's also a few other products that aren't available yet on the dashboard.
Google says, at the bottom of the page, "This page represents the data associated with this Google account. All data is private unless indicated with (an) icon as visible to others". Next to every entry in the list is an option to manage that information and modify it.
There's a video that explains the system in more detail, which we're currently trying to track down (Google's removed it from YouTube) but probably a better way to understand it is to go visit Google Dashboard yourself, and see exactly what the big G knows about you. You might find it scary.
UPDATE: We found the video. It's embedded at the top, there.