The Google toolbar reports URLs back to Google if you have page rank or a few other features turned on. Their privacy policy says that they store the URL and provide you with whatever feature you requested, but it doesn't say weather they do anything further with the data.
Relevant bits:
URLs and embedded information
Some of our services, including Google Toolbar and Google Web Accelerator, send the uniform resource locators (“URLs”) of web pages that you request to Google. When you use these services, Google will receive and store the URL sent by the web sites you visit, including any personal information inserted into those URLs by the web site operator. Some Google services (such as Google Toolbar) enable you to opt-in or opt-out of sending URLs to Google, while for others (such as Google Web Accelerator) the sending of URLs to Google is intrinsic to the service. When you sign up for any such service, you will be informed clearly that the service sends URLs to Google, and whether and how you can opt-in or opt-out.
For example, when you submit information to a web page (such as a user login ID or registration information), the operator of that web site may “embed” that information – including personal information – into its URL (typically, after a question mark (“?”) in the URL). When the URL is transmitted to Google, our servers automatically store the URL, including any personal information that has been embedded after the question mark. Google does not exercise any control over these web sites or whether they embed personal information into URLs.
We process your requests in order to operate and improve the Google Toolbar and other Google services. For example, by knowing which web page you are viewing, the PageRank feature of Google Toolbar can show you Google's ranking of that web page. And the Sidewiki feature can tell you if others have written Sidewiki entries on a given page. Likewise, by processing the text on a web page, SpellCheck can offer spelling suggestions and AutoLink can provide useful links to information.
Relevant bits:
URLs and embedded information
Some of our services, including Google Toolbar and Google Web Accelerator, send the uniform resource locators (“URLs”) of web pages that you request to Google. When you use these services, Google will receive and store the URL sent by the web sites you visit, including any personal information inserted into those URLs by the web site operator. Some Google services (such as Google Toolbar) enable you to opt-in or opt-out of sending URLs to Google, while for others (such as Google Web Accelerator) the sending of URLs to Google is intrinsic to the service. When you sign up for any such service, you will be informed clearly that the service sends URLs to Google, and whether and how you can opt-in or opt-out.
For example, when you submit information to a web page (such as a user login ID or registration information), the operator of that web site may “embed” that information – including personal information – into its URL (typically, after a question mark (“?”) in the URL). When the URL is transmitted to Google, our servers automatically store the URL, including any personal information that has been embedded after the question mark. Google does not exercise any control over these web sites or whether they embed personal information into URLs.
http://www.google.com/privacy_faq.html#toc-terms-urls
Uses
We process your requests in order to operate and improve the Google Toolbar and other Google services. For example, by knowing which web page you are viewing, the PageRank feature of Google Toolbar can show you Google's ranking of that web page. And the Sidewiki feature can tell you if others have written Sidewiki entries on a given page. Likewise, by processing the text on a web page, SpellCheck can offer spelling suggestions and AutoLink can provide useful links to information.
http://www.google.com/support/toolbar/bin/answer.py?hl=en...