I have been having trouble with MiWi. It seems to require me to reboot both devices (Macbook Pro and iPhone) before being able to connect via Wifi. If I don't, I can see the Wifi AP, but not connect.

However, USB tethering seems to work just fine. USB is fine for the MBP, but when I get an iPad, I will need the Wifi part of it to work occasionally, as I don't want to pay for 4G service on the iPad, 3G from the iPhone is fine.

It's an AT&T iPhone 4S 64GB, 5.0.1 with Absynthe.