This document (PDF, from Wired.com) is pretty fascinating. It teaches IRS employees how to use the internet for researching tax cases.
This reminder is on the second page:
You are not completely anonymous on the Internet. Website logs track your IP address, last site visited, type and version of browser, and date and time of request. IP addresses can be traced back to the Internet access provider or organization that controls the IP address, i.e., 22.214.171.124 through 126.96.36.199 are assigned to “irs.gov”.
But apparently there is an “Internet Content Filtering Change Request Form” (long enough name for you?) for employees that need to access sites that block irs.gov IP addresses.
Regarding social networking sites:
Employees may not use either their correct identification information or false identification information to become “friends” to gain access to the taxpayer’s social network site.
Other information includes using Google advanced search, Google street view, social networking sites, archive.org, search engine caches, and WHOIS searches.