I have also tried to use my n900 as a 3g modem for Nexus 7. I followed the steps in the janszoon's post but I can't get the PAN connection between the devices established. Nexus 7 is not showing the option to use the bluetooth connection for internet (or at least I can't find it). N900 says in the bluetooth setup GUI that the supported profile is OPP and bnep0 is not shown in ifconfig. I had the devices paired already before installing the scripts, but I also tried to pair them again. This did not help either. Any suggestions what might be the reason?
DisablePlugins = network,input,hal
DisablePlugins = hal