Nit:
You can also play around using this [base JSFiddle](http://jsfiddle.net/vjeux/25Rhk/).

Ever so slightly like this wording more =P...

It might also be good to put this right after the "fastest way to get started" section:

## Installation

The fastest way to get started is to serve JavaScript from the CDN:

```html
<!-- The core React library -->
<script src="http://fb.me/react-0.3.0.min.js"></script>
<!-- In-browser JSX transformer, remove when pre-compiling JSX. -->
<script src="http://fb.me/JSXTransformer-0.3.0.js"></script>
```

Or you can play around using this [base JSFiddle](http://jsfiddle.net/vjeux/25Rhk/).

...