I just tried it.
My steps:
-Created a new network on my MacBook named "iPhone Test" w/o password
-went to my network settings on my iPhone and connected to "iPhone Test"
-opened Air Sharing on my iPhone (note: at the bottom, it showed my air sharing address)
-I attempted to open Google on my MacBook using FireFox
Results:
-I was unable to connect to the internet on my MacBook from my iPhone using these steps
+My iPhone is not jailbroken
+My iPhone said I was on 3G
+I have a flat black MacBook Core 2 Duo
Am I doing something wrong or is anyone else getting the same results as me?
Same results as you.