I posted this question about 3 pages ago ("What is your Holy GRail of GTD?") and got some great answers. Here is what I still stand by today:

My Holy Grail of GTD is reflecting time. If I can get the Weekly Review done and still have time to actually think about the work I have to do/most want to do I am happy. Since I started GTD this Jan, I have noticed a dramatic increase in the number of creative and courageous ideas I have had for 2012. This week I have an hour planned to reflect on a recent event I completed (thank you notes, incidental receipts to submit, lessons learned, next time do this, etc). I scheduled that during my WR, instead of reflecting during the WR.

But do check out that thread titled Holy Grail to hear more.