I worked on screen saver engines that had to support these - We did a lot of direct access to the bit mapped display for speed, at the cost of compatability. Th

I worked on screen saver engines that had to support these - We did a lot of direct access to the bit mapped display for speed, at the cost of compatability. That being said, there were OS hooks that made responding to the rotation easier. The problem came in when running applications that didn't respond correctly to the configuration changes - since we had patched the os (transparently, particularly when not actually driving the display) we got blamed for a lot of application crashes and ended up debugging and sending very explicit bug reports to other software vendors. When the iPhone came out, I was deathly afraid of the screen rotation for about 6 months, convinced as I was that 50% of the apps wouldn't respond gracefully. (And I personally have never found one that failed here.)