Well so far these are the problems I have with my n900 physical wise after 3 months of use:

• Slider is getting a little wobbly and stiff
  Slider is scratching my device
  Screen has a creak when I tap it on the top right.
  Bright spot on the LSD
  The power button has started to go a little in the device. Harder to press.
  Left part of volume key is also a little loose and harder to press.

I can deal with everything above because im used to nokia sloppy workmanship but if my Usb port breaks. That would be it for me. really hope it doesnt.