Google has a long history of tracking user activity, and the introduction of its Chrome operating system later this year is sure to follow suit.
Google personalized Web search--Google's bread and butter business is its search engine, and its personalized search is a way to put a face on the data. When you're signed in with your Google account you can opt in to having your Web history tracked; Google archives all of the sites you've clicked on from search results, as well as what time of day you clicked on them.
For those who are not signed in, the company uses identifiers like cookies and IP addresses. But when you're signed in it can actually aggregate that data no matter what computer you're on. With a system-level log-in, it could theoretically do this no matter what browser you're using, giving Google a far richer set of data.
Chrome browser--When Chrome was first released, Google got in some hot water over its terms of service, which stated that Google had the rights to license any content that went through the browser. It quickly backtracked on the claim, citing that the terms heavily borrowed from other Google products and that it didn't make sense for Chrome. This would have given Google licensing control over things like user photos, videos, and words.
The one area where Google's Chrome can still access some of that information is with its reports system. This is an opt-in program for users to provide Google with crash reports and detailed information about what features they're using. Google has said this does not include any information from form fields, or from users' Google accounts. However, it does track what sites and search terms you've entered into the address bar.
Gmail--Google's Web mail service was one of the first Web mail services to provide contextual advertising, meaning it actually goes through your e-mail messages to give you advertisements that match up with a conversation you're having. Did you mention skiing in that last e-mail? Don't be surprised if you start seeing ads for local lift tickets or a new pair of ski boots.
Google Checkout--Checkout is Google's online payment service. It lets customers pay for items using credit cards or bank accounts that are tied to their Google credentials. As far as collecting information goes, Google holds all of a customer's financial information on its servers including name, address, and account numbers. It also tracks how quickly they type in that information when making purchases, which account they used to pay for the good, and what that good was, giving the company a broad overview of a particular customer's purchasing habits.