Here is a pic of the actual usb port on the main board of the N900.
As you can see the pads holding the jacket of the port itself are way way too small for a usb port and is clearly a design fault also it is surface mount and no through hole at all in the design as it fully relies on the 4 corner soldered points , the underside adhesive applied during assembly and the 5 data/charge points at the rear of the port.
The obvious fault that occurs is the usb port detatches itself from the m/b (motherboard) because of insufficient hold on the m/b but before it does, dry jointing occurs and the very reason a "wiggle" is needed to get the charge or data flow to work (this action in fact makes the process of detatchment terminal).
I would NOT reccomend anyone even try a repair or a fix whilst in warranty as this will for sure invalidate it (nokia aint stupid and can easily tell if its been worked on at all).
In the future when all warranty has expired it is easily possible to actually solder an external usb port via a lead soldered directly onto the 5 points at the rear.
Hope this is helpful.