Some of the fillers are actually based on stories from the novel(s), like the one where Kanda goes to that village with the "witch". I wonder if quality of the filler correlates.

I'm still uncertain if I'm going to buy it when it's released. As much as I love the manga, I just can't get that enthused about the anime; I still haven't watch most of it. Plus, there are other box sets I still want to get (Saiyuki, Inuyasha, DNAngel) so D.Gray-man will be going to the bottom of that list.