Actually that's an interesting point, because Google Apps don't do that. If you're in Gmail and you open a spreadsheet, it opens in a new Window/Tab, so that it has an independent history. Ditto if you click on a link in an email. This approach gets you separate histories for your apps. You don't get an awkward single history that links across your mail and spreadsheets and random websites. You get separate histories. The exceptions are when you choose to manually enter a new URL, or if you hit back enough it will take you out of Gmail into whatever you were doing before.