I run Ubuntu as my main OS. Then I have VirtualBox running with couple Windows virtual installs and a couple Linux virtual installs. I give about 5G-10G disk

I run Ubuntu as my main OS. Then I have VirtualBox running with couple Windows virtual installs and a couple Linux virtual installs. I give about 5G-10G disk space to each, and about 500M to 800M RAM to each (my work laptop only has 2GB, so I have to be careful). The windows virtual installs are for running different versions of IE and programs like Photoshop. The Linux versions are for running things I don't want to conflict with my main Ubuntu system. For example, I use rvm for Ruby programming, and wanted to try rbenv. However, I heard they don't play well together, so I installed rbenv on one of my virtual Linux installs and was able to experiment right away without worrying about messing up my rvm configuration. Another time, I was learning about certificates and keys, and did not want to screw up my current configuration on Ubuntu, so I was able to experiment on on of my Linux virtual installs instead, with no harm done to my main Ubuntu system. It's very liberating to be able to experiment with these without worrying about affecting your primary system.