I had two issues with JetPack – but I finally got it working.
Issue one –
Jetpack could not contact WordPress.com: register_http_request_failed.
This usually means something is incorrectly configured on your web host.
Operation timed out after 15000 milliseconds with 0 bytes received
This was resolved by setting the max_execution_time to 300 in my php.ini file – make sure you restart your webserver / fast cgi daemon.
Issue two –
Your website needs to be publicly accessible to use Jetpack:
Error Details: The Jetpack server was unable to communicate with your site [IXR -32300: transport error: http_request_failed Operation timed out after 15000 milliseconds with 0 bytes received]
This was easily solved by changing the following value from 1 to 2 in my /etc/init.d/php-cgi script