The common problem with N900 is that, due to frequent usage of micro-USB cable, the micro-USB port becomes separated from the device. It is caused by strong cohesion between the micro-USB cable and micro-USB port (N900 can literally hang on the cable; I have observed it a couple of times myself, after accidentally knocking N900 off the table). To reduce the cohesion - to make it easier to take cable out of the N900 without damaging the port - it is suggested that the 'teeth' on micro B USB plug are removed.

P.S. Generally, the micro plug design is rated for at least 10,000 connect-disconnect cycles which is significantly more than the mini plug design. It is also designed to reduce the mechanical wear on the device; instead the easier-to-replace cable is designed to bear the mechanical wear of connection and disconnection. That's why my micro-USB cable is starting to fall apart, while micro-USB port of N900 is fine.
But still, I have heard of the falling out micro-USB port of N900 so many times, that I warn you: be careful and gentle with it. Be prepared for the possibility of it falling out. Be aware that some people literally soldered it back. And once upon a time, an inductively-charged N900 was made.
Best wishes.