iPhone tethering not working via bluetooth
This fixes what i presume to be a corrupt internet sharing preference file. It will also remove all other network settings such as wifi access-points and their passwords so keep that in mind. Other data such as pictures and contacts will be completely safe.


On your iPhone, go to Settings -&gt; General -&gt; Reset and choose Reset Network Settings. 
The iPhone will ask you to confirm and then restart.
In Settings -&gt; Internet Sharing reenable it and choose to turn on bluetooth if a dialog asking to do so appears.
Reconnect to your wifi-network if applicable.
You're probably done, try connecting. If it doesn't work go on.
In Settings -&gt; General -&gt; Bluetooth tap the blue arrow beside your computer and choose to forget the device.
On your computer go to System Preferences -&gt; Bluetooth and remove your iPhone from the list.
Go to System Preferences -&gt; Network. In the Location drop down choose Edit Locations.... Add a new location and press done.
Make sure the new location is selected and press Apply.
Go back to System Preferences -&gt; Bluetooth and re-pair your phone to the computer.
Connect to your iPhone's bluetooth network.
Back in System Preferences -&gt; Network if you do not have a Bluetooth PAN interface add it by pressing the + button in the lower left.
Press Apply and cross your fingers.


Doing the first five solved it for me, after one year of broken bluetooth-tethering.