Members of our own forums, as well as others around the web, are not thrilled with iOS 4.3. Engadget has posted a video showing some of the pixel problems. Other issues noted by viperGTS include poor performance of the Springboard, slow app updates and quitting of apps, the home button being unresponsive and poor music playback. Even more critical errors have occurred including the inability of iTunes to recognize the device, as well as the loss of mail, contacts and other personal data. One user reported being unable to even turn the device on, as the sleep and home buttons are no longer operational.
In any case, it would seem best to wait for an update before upgrading to iOS 4.3, or downgrading if you can (hope everyone backed up those blobs!).