I have a pretty similar setup for GTD.
Mine consists of Inbox, Later, and Waiting for someone. I use the Inbox as next actions because moving it from Inbox was just more work for me than needed. I also use the calendar feature for my next actions on the items in the Inbox, so they are date related and it's easy for me to tell what to do next, and when. Waiting for someone is jump linked to a person (like your setup), so I can easily tell who I need to follow up with. I usually have a calendar event to follow up, as a reminder. So far it's working very well for me, as I can link items to files, folders and related projects. It gives my GTD system a level of context that I haven't been able to recreate in any other program, and is the key piece that really sets PersonalBrain above everything else I've tried (including MindManager). The feature that brought PersonalBrain back from the dead and replace MM again was the calendar. In 3x, keeping track of date related items was just too unwieldy. I'm really looking forward to the improved tagging feature. I think it will bring a whole new depth to thought relations and retrieval.
Java SE 6