I upgraded my iPhone to OS3 on June 19th and everything works - for the most part - except for one persistent aggravation that I encountered after the upgrade.    The problem was that the iphone would no longer connect known WiFi networks automatically as they did with the previous OS.  After a quick Google search, it seems to be a problem with other iPhone users too.

 To fix this annoyance, navigate to:

1. Settings
2. General
3. Reset (at the bottom of the General menu)
4. Reset Network Settings

The will restore the phone's default network settings which means you'll have to re-enter any saved network passwords.  After the reset, the phone is connecting to my home network just like it always did before the upgrade.