I've been using GTD for about 18 months now using Outlook tasks and just transitioned to Toodledo in the last few days. Toodledo supports the GTD model perfectly.
I feel the frustration of others regarding managing Project tasks in the GTD model and thus also in Toodledo. I made this process work using Outlook tasks, prefixes, and categories (similar to tags that can be assigned to more than one project).
I challenge the development community to use Toodledo's APIs and incorporate functionality for project management "best practices" in way that is simple, efficient, and effective. For now, I will use tags and prefixes to support project management in Toodledo but will continue to look for a single tool that supports both GTD and Projects efficiently and effectively and support across all major platforms (iOS, Android/Linux, and Internet).