i just received my durasec hightec screen protectors (its 2 u get) for the n900. I took the high durable one, and i cant say anything about how much it decreases the sensitivity.

i asked this myself in another thread as well, with someone replying that the sensitivity is close to not altered by the screen protectors from durasec.

though i checked the protector out and it is like 1/3 to 1/2 a millimeter thick. which is.. offcourse 'an' obstruction for the touchpad i think. not much but i think it will affect it slightly.