I actually just bought a Grifiti fat wrist wrest for both my keyboard and for my mouse at work recently. I have been using them for about two months and had to shelve them today as I'm getting some pain in my right wrist which I never had before.
I've found that the wrist pad is coupled with your posture and height in relationship to your elbows. I had the fat graffiti palm rest and I did not like it because it was too deep (front to back) for me since I often have my elbows below keyboard level. When sitting like this, the wrist pad would dig into my wrist and NOT be ender my PALM which I think is what was leading to quite a bit of discomfort.
I ended up making some wrist/palm rests out of wood that measures 3/4" x 2 1/2". I put some felt pads underneath as feet and I found that if you get the height to align with the edge of my keyboard they have been fairly comfortable even if my elbows are somewhat below keyboard level. I think the main reason this is comfortable is because that the edge of my palm is resting on it and NOT my wrist. I also use this when I'm at my standing desk which was measured for my elbow height.
This is at work, and somewhat cluttered:
Closeup of the side to show how the height matches the keyboard: