Findings with iOS 4.3:
- Personal Hotspot is enabled on 3UK on the iPhone 4 ("The One Plan" SIM only, £25pm).

Can turn it on and off at will.
- When connecting an iPad to the iPhone 4 via Personal Hotspot, you get a cool looking personal hotspot icon at the top left instead of the standard WiFi icon. A nice touch.

- Location data seems to be transferred to the iPad aswell. Loading maps on the iPad while tethered shows my current location.
- When tethered via personal hotspot, there doesn't appear to be the arbitrary 20mb download limit seen on other iOS devices when connected via 3G.
- AirPlay seems more reliable. I can reliably, and without fail, transmit 720p video from iTunes on my MacBook Pro to both my iPhone and iPad (Using the AirPlay app) without stuttering.

- New home share functionality is SWEEEEEEET. All iTunes videos and music available in the native apps, without needing to sync them first.