Well 0.4 is kind of living on the bleeding edge unless I'm mistaken? The npm package for grunt is currently on 0.3.17. The official site also points to the stable 0.3 docs so that should also abate the confusion somewhat.

Personally, I've just stuck with 0.3 (despite the constant temptation to check out the latest version!), it's got all the tasks I need for my workflow and it is otherwise flawless.