This is a very old thread, also addressed elsewhere. There is a video on YouTube of someone who disassembled the Kindle 3 when looking for the solution to the reset problem with the optional cover. In that video, it is very clear that the switch is a simple plastic switch sliding in a plastic track. Although it is possible that dirt accumulation could cause the switch to drag a bit, it is also clear that the return spring is isolated from the switch such that it is not likely ever to break or lose tension over the life of the Kindle 3.
If the switch drags, use your fingernail to move it sideways, do not press upward while simultaneously trying to move it sideways. It's a simple matter of vectors -- if you want it to go sideways, push it that direction, not upwards at the same time. It is virtually impossible that the switch would wear out or stick if kept clean, and cleaning it should be simple enough with compressed air in extreme cases. If you pour sticky liquids in there, you are at fault -- good luck.
I have two K3's and no problems with either of them when pressing the switch in the intended direction.
