What you need to know about Asynchronous JS Programming?

I'm a web apps developer, I use for most apps PHP/MySQL with APC enabled, caching technologies: Memcached is my favorite one. Sometimes I use Percona MySQL version.

I'm new to NodeJS and I want to build my own web app using it. It's a SaaS working with Facebook, Twitter and Instagram APIs. I read a lot of good things about it.

What I need to know about Asynchronous JS Programming before starting the app?

Is there any performance advantages for Asynchronous Programming?

Is there any live examples, graphs with the difference between Async/Sync?

It doesn't block.

Let's compare with PHP:

<?
    readfile('some/large/file.bin');
?>

This might take a while. And while PHP reads the file, it won't be able to do other stuff (like answering other requests).

The same thing asynchonously (using node.js):

fs.readFile('/some/large/file.bin', function callback);

Node does the reading without blocking the current process.

So in conclusion: while the synchronous way blocks the process until the result is available, the asynchronous method has the advantage of doing other stuff, even before the readFile callback got fired.