I've had the most interesting variation of results with USB-charging and the N9. The original nokia cables seem to work with PC-USB-ports but not with 3rd party solutions. Generic cables with PC-USB are recognised as data but not charging cables, etc. etc. I even filed a bug:

http://harmattan-bugs.nokia.com/show_bug.cgi?id=1098

This in connection with the battery management bug (suddenly dropping to 4%, not charging fully) are the most serious bugs Nokia never bothered to fix. I'm half of a mind to sue them for it (I still have warranty on my devices).