Serge is a French photographer living in Paris who has produced a series of free YouTube videos around post-processing in Lightroom and Photoshop. Well worth a watch, as are his paid video collections too! I've learned a huge amount from his weekly free podcasts - this is one of the best resources out there to learn retouching skills.
His main website is at www.photoserge.com
His YouTube channel with his english tutorials is at http://www.youtube.com/user/cmoeu