Some of the newer HP keyboards are designed really wierd, especially those at my job. Lying them flat actually leaves the upper row of keys feeling like they are actually lower then the front keys. I have to raise these boards to make them work for me. Too bad I can't have my favorite keyboard at work. These HP keyboard are absolutely some of the worst I have ever used. And yet, I see our agents using them flat. I guess they like it that way, but for me, I have to have some angle.
My model M though is another story. With it, I leave it flat because the keyboard was designed a lot better than the HPs. The model M has a natural curve in the keys that keeps them at the perfect angle for me. Raising the model M just puts too much angle on the rear keys.