This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
I have Ubuntu installed to a USB flash drive. It's a handy way to take your personalized environment with you to other computers. Unlike a Live CD, you can do updates and save documents. Look here for a walk-through of the process.
Of course, you give up some performance using an external drive. Whether it is advisable or not depends on your requirements.