Advantages of using React:

• easy to know how a component is rendered, you just look at the render function.
• JSX makes it easy to read the code of your components. It is also really easy to see the layout, or how components are plugged/combined with each other.
• you can render React on the server-side.
• it is easy to test, and you can also integrate some tools like jest.
• it ensures readability and makes maintainability easier.
• you can use React with any framework (Backbone.js, Angular.js) as it is only a view layer.

What is not so good about React?

• it is only a view layer, you have still to plug your code for Ajax requests, events and so on. Some people get surprised by that.
• the library itself is pretty large.
• the learning curve can be steep.

If react-native is really how it was described, react is going to become even bigger.

Performance wise, it is really good as it relies on a virtual-dom to know what is really changing in your UI and will re-render only what has really changed. It does have trouble with very large, slightly changing, lists of children (2000 <li> test), but can be optimized simply.

If you are not sure, just think about the big projects using React: instagram, hipchat, facebook chat and so on.

Some resources:

• React for the stupid people
• Rebuilding Hipchat with React
• Why React?

And probably one of my favorite blog post Why React is awesome?