Caching proxy and Anonymizing proxy

Caching proxy :
A proxy server can service requests without contacting the specified server, by retrieving content saved from a previous request, made by the same client or even other clients. This is called caching. Caching proxies keep local copies of frequently requested resources, allowing large organizations to significantly reduce their upstream bandwidth usage and cost, while significantly increasing performance.There are well-defined rules for caching. Some poorly-implemented caching proxies have had downsides (e.g., an inability to use user authentication).(Known HTTP Proxy/Caching Problems)

Anonymizing proxy:
An anonymous proxy server (sometimes called a web proxy) generally attempts to anonymize web surfing . see above orkut proxy examples ie, act as a anonymizing proxy.These can easily be overridden by site administrators, and thus rendered useless in some cases.
Access control: Some proxy servers implement a logon requirement. In large organizations, authorized users must log on to gain access to the web. The organization can thereby track usage to individuals