I do agree with a number of replies here. I' ve installed every plugin for Outlook and tested every little hack. I got very tired, my outlook instable and my computer slow. So the best approach remains a clean Outlook with a good folder structure and best use of "on-board hacks" such as rules and macros.

I've also tried the GTD plug-in with a similar effect like above. However, some functionality I liked so I just did some smart macro and rule setup that, for example allows me to store @WaitingFor messages (so tasks I delegated by mail) in a dedicated folder and automatically create a task in my task overview, context '@Waiting For'. Have a look at my blog reliabledisappointment.com where I describe my setup and provide the simple macro code.