I'm finding that Codio is running a little spotty. Sometimes it works, other times it dumps. However, I was able to get familiar with what is needed to work with and compile ML and I was finally able to get it working on my MacBook--no virtual box necessary.
In any case, compiling in the cloud is a good starting point for users that don't have a complete development platform to work with. Too bad that Codio started locking out new users from some of the feature needed to compile ML.