I don't really see how it is that complicated. I have a BB 8700 and the task application is just about everything I need. The only thing it can't do is mark tasks as private (altough you can make appointments private). I use the Private flag to separate personal actions from professional actions.
But it does categories and lets you filter the task list by category (great when you are working in a particular context).
I am using the 8700 synched live with Outlook 2003 with no third-party plug-ins (just configured Outlook per recommendations in the white paper) and I feel that I have everything I need to apply the GTD system 100%.