yes,...I do it also that way....

-connect usb
pcsuite-mode
-on n900:
sudo gainroot
ifup usb0
check the internet connection for 'dummy network'
check the DNS in resolv.conf
-on PC:
set/use USB-IP in same range (ifconfig)
open ports by adding iptables-forwarding for usb-ip's

...now you have an internetconnection and you can ping ex. www.nokia.com

I am porting the GUI by a VNC-server on my N900 and my VNC-client on my ubuntu can login by usb

changing addressbook or installing apps on my PC for my N900 is now possible

regards
schasch