Avatar.js

import React from 'react';
import md5 from 'MD5';

class Avatar extends React.Component {
  static propTypes = {
    email: React.PropTypes.string,
    size: React.PropTypes.number
  }

  static defaultProps = {
    size: 32
  }

  render () {
    var { email, size } = this.props;
    var hash = md5(email);
    var src = `http://gravatar.com/avatar/${hash}?s=${size*2}`;
    return React.DOM.img({src, size: height});
  }
}

const is too long to type, I use let and it makes me feel a little bit I code in ML

Also, why no JSX?

Is it just me or size: height}); needs to be height: size});