Inspiration is a lovely piece of software primarily designed to introduce the concepts of mind mapping, brainstorming, and outlining in the classroom. It lacks the tools required to really make it a GTD tool. At the risk of sounding like a fan boy, this is what you pay for when you buy MindManager - extensive integration into Office apps that let you actually do something with the results of your work by getting it into your system.

If you're a practiced GTD'er with a stable system, the combination of MindManager and ResultManager is well worth looking into. It's not cheap. But it does provide a level of visual organization and display that no other software solution I've found can match.