The new toolbar version from Google helps the browser who landed on an error page to find an alternative URL by suggestions. The page displays an alternative URL and asks if you searched for something similar to it. If not, the error page also provides suggestions and also provides a Google search box.
However, this replacement by Google on a website with their own 404 page is also voiced as unethical. This is viewed by many webmasters as an intrusion. The new beta toolbar also produces similar results while an non-existent domain name is searched for. Also, when a page is temporarily unavailable or if the server is down, the Google toolbar displays the cached page instead of the live page.
New Google Toolbar handles 404 Errors
