iPhone 3GS, iOS 6.01
Macbook Mac OS 10.6.8
The iPhone 3GS hotspot works fine via Bluetooth, connected to my iPad.
If, instead, I tried it with my Macbook via USB (can't do it via Bluetooth for another reason), if I open the network preferences I can see the iPhone but it says that the cable is not connected or the device is not responding. Of course the cable IS connected and iTunes correctly sees the iPhone.
I've never tried tethering before on my macbook. I haven't tried other solutions.