sometimes the solder spots on the prints are not what they need to be. i had a n96 with the volume button broken off the print. they fixed it right away in a service center. i guess they can do this too with the n900 if the USB connector get loose.

Im more worried by the flexcable connecting the screen to the main board. most of these flex cables die within one year of extreme use. (and im an extreme user!) A friend of me bought my n95 and his flexcable was broken within one week. (just sold it in time )
The flex cable is pretty tight between upper and lower part of the device resulting in making the flexcable bend to its limits everytime its opened and closed