@JAV, You may also have to worry about Toolbar programs (like Alexa toolbar, Ask toolbar, Bing tool bar, Yahoo Tool Bar, Google Toolbar, lots of Firefox plugins).  I believe that some of these send URLs back to the "mother ship" to help with page rankings and site analytics.

But Instawallet is a very nice looking site!

See http://www.google.com/privacy/faq.html#toc-terms-urls

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.