Update to our previous iOS 4.3 post: iOS 4.3′s new Personal Hotspot works on iPhone 3GS – albeit only with cable and Bluetooth pairing!
Long-time friend Enrico has just tested iOS 4.3 on an iPhone 3GS and checked that Personal Hotspot, the internet connection sharing feature of 4.3, runs happily although only via the iPhone cable or a Bluetooth-paired connection.
So, as far as we know, Wi-Fi sharing is available only for iPhone 4.
As a result, iPhone 3GS users can still enjoy their beloved toy and share connectivity to iPad (non-3G) or …

Apple iOS 4.3 is now available for download from Apple for all iPad, iPhone 4 and 3GS, iPod touch (3gen and 4gen)!
We’re now testing and trying out all new features and will report soon.
A brief feature list include:

improved Safari Javascript engine and overall speed
Airplay: now greatly enhanced and available to most multimedia devices in your home!
iTunes sharing (at last!)
Personal hotspot (iPhone 4 only): the perfect solution to turn your iPhone 4 into a wireless gateway for all devices (and get over tethering).