Very interesting. It is mostly harmless stuff, but it is surprising how much information is retained via Google Checkout, Gmail, Maps, Picasa etc.
I suppose it is the price we pay for convenience and we have to rely on Google data remaining secure on its servers. That is not a gimme judging by data losses elsewhere e.g. Sony. I shall not lose any sleep over it, however.
If you don't have a google login there will be no way of google relating information to you between sessions if you delete the google cookie.
Personally I like the convenience of having a google login as it lets me check my email anywhere, plus keep my calender synchronised between my work PC, home PC and mobile.
I also like, but find it vaguely disturbing, the fact that google knows where I am when using my mobile, so the weather forecast is based on my current location, and search results are sorted by location.
If you have an account, logging into the dashboard will allow you to delete any and all information you wish to dispose off...