To help spot problems, Facebook employees who access the social network from within the company's internal network will always see an experimental build of the site based on the very latest code, including proposed changes that haven't officially been accepted.
Probably the only place where your excuse for checking Facebook at work can be "Looking for bugs!"
The many data sources tracked by Facebook's internal monitoring tools even include tweets about Facebook. That information is displayed in a graph with separate trend lines to show the change in volume of positive and negative remarks
Guess I need to tweet more about how slow their mobile app is getting...
One of the major ongoing development efforts at Facebook is a project to replace the HipHop transpiler. Facebook's developers are creating their own bytecode format and custom runtime environment.... the company can push thin bytecode deltas representing just the parts that have changed. Facebook may even be able to splice the updated bytecode into the application while it's running, avoiding a process restart.
Even though I'm doing nothing nearly this awesome, this article has done more to inspire and excite me about my own coding than anything I've read in a long time.