We collect and log the Internet Protocol address (IP) of all visitors to ClevelandSpineIntitute.com. An IP address is a number automatically assigned to your computer whenever you access the Internet. IP addresses allow computers and servers to recognize and communicate with one another. We collect IP address information so that we can properly administer our system and gather aggregate information about how our site is being used, including the pages visitors are viewing. This aggregate information Will Not be shared with advertisers, sponsors and other businesses. To maintain your anonymity, we do not associate IP addresses with records containing personal information. We will use IP address information, however, to personally identify you in order to enforce our legal rights or when required to do so by law enforcement authorities such as an NSL (National Security Letter). You should be aware that a significant amount of data is transfered and collected with every page request and that data may be stored, cataloged, and stored on our servers or compiled in internal reports.
Wikipedia offers a good reference on header fields and the information contained and recorded.
(For More Info See: http://en.wikipedia.org/wiki/List_of_HTTP_header_fields).