Many large corporations block those as well. Partially it's to prevent goofing off, but I suspect (especially in the White House) the main reason is documentati

Many large corporations block those as well. Partially it's to prevent goofing off, but I suspect (especially in the White House) the main reason is documentation. Pretty much all communications coming in and out of the WH have to be monitored and recorded - either at the summary level (sender/recipient/subject/date) or at the full-text level, owing to laws about public access and documentation in the National Archives. Interested parties can FOIA pretty much anything produced by an employee of the government; electronic communications are no exception. So until NARA can created a Twitter/Gmail/Facebook proxy - for which I wouldn't stay up waiting - I suspect they'll just keep blocking them.