What are different sources from where I can learn Hadoop and MapReduce from a practical point of view?

From your question, it seems you have theoretical knowledge at this point of time and want to gain some hands-on experience. Below are couple of pointers which may help you, though I doubt you may have already came across some of them- 1. Trainings: There are hands-on trainings conducted by Cloudera and Horton works and based on your interest(administration or development) you can choose the track. 2. Books: I think http://www.amazon.com/Hadoop-Practice-Alex-Holmes/dp/1617290238/ref=sr_1_3?s=books&ie=UTF8&qid=1385271632&sr=1-3&keywords=hadoop will also help a bit, but it isn't limited to Hadoop or MapReduce, but also various other tools like Pig, Hive around the Hadoop ecosystem. 3. Github: There are few repos on github as well which may help - https://github.com/hortonworks/hadoop-tutorials, https://github.com/romainr/hadoop-tutorials-examples.

You can refer some informative http://blog.simplilearn.com/big-data/impact-of-hadoop-on-big-data-and-global-business-performance and http://www.simplilearn.com/resources/videos?category_id=16  available on the internet to understand the basic concepts. I have come across a useful resource for the http://www2.simplilearn.com/acton/fs/blocks/showLandingPage/a/9696/p/p-002a/t/page/fm/0?utm_source=Facebook-Posts&utm_medium=Big-Data-Ebook&utm_campaign=Big-Data, found it very interesting. Content is well structured and easy to understand, helped as a hand guide to understand the key features of Big Data and Hadoop.  And also you can try and attend the http://www.simplilearn.com/resources/upcoming-webinar. Besides you can plan to take up the http://www.simplilearn.com/big-data-and-analytics/big-data-and-hadoop-training-online/ppa272da30 to get expertise and master the skills. Here is an interesting video for the reference.