Right now it looks like you are using Ubuntu's default Apache2 + PHP5 packages. The site seems to be taking a hit with the thousands of people coming in from Reddit and other forums. Pages are timing out and the site is not responding.
In the future I would change the stack to nginx + php5-fpm with Varnish cache running in front of everything.
Or maybe just keep apache2 and throw Varnish in front..
Regardless, you should always have some sort of caching software in front of a web app. This will put less strain on the server CPU so that whenever someone visits the site, PHP won't have to recaculate everything and generate the HTML again. Instead, it can just be pulled instantly from the memory.
You can use any kind of caching software, but I always recommend Varnish cause it's dead simple to setup.