yes it is and, in my opinion, it is complex.
So while working with GTD for about a year now ( and infecting others too), i like the system, almost nothing falling through the cracks.
Most difficulties i experienced were with capturing commitments made during conversations. And then not the larger formal meetings but the fast encounters with people i work with.
I'm about 50% of the time at the office and the other 50% on variable sites. So mobile is very important to me. And to drag a tablet or laptop everywhere (along with a writing pad, camera, measurement stuff (tape and digital) just isn't practical.
So by using a "smart moblie phone i do get almost all commitments and the mobility i need. It's just doing things double or too with too many steps at times which i do not like.
The other limiting factor is the people working for me at the office. They work with GTD now, have outlook but do not need the mobility. And to change everything just for my sake (with the amount of errors expected from change) just isn't right.
so a small tweak in which OneNote mobile connects to Hotmail of vice versa would be great.