I think the issue is that the home/phone/left buttons and the right/back/end buttons each have only one actual button beneath them. (See the internal photos at
this webpage.) The device uses a capacitive sensor to detect which area is being pressed. If you wear gloves, use your fingernail, or have really dry fingers, the capacitive sensor won't work.
To get a feel for how your capacitive sensor works, or to see if it's defective, use the "Nav Debug Tool" in the following package:
http://wiki.xda-developers.com/index...d_Testing_Tool