We recently re-developed an application that was originally built using ASP Classic and MS SQL Server and converted it into PHP/MySQL and along the way, one of our goals was to simplify the search system. The original application had individual searches for specific content types -- for example, if you wanted to search for documents you would have to browse to that area and click the search drop-down. The fields listed there would be things like document title, date posted, document type, etc.
It's pretty common to use Google Adsense to serve ads on your site to generate supplemental income. But if you run a membership driven or e-commerce website, you may decide that you want to hide ads from those valuable users/customers and only show them to anonymous users. Doing so in Drupal is very easy, particularly if you have placed your ads in blocks.