I presume the instability of the driver has more to do with user system settings. It has been said already that fglrx is only tested on a handful of distros, and I doubt every single form of hardware combination is tested. The various user experiences with the driver is evidence of that; if the driver just plain sucked and was broken no one would be able to use it successfully.
As for the documentation for settings, it has also been explained on a previous discussion here on the forums. I for one, think that all functions and parameters available for a particualr driver release are automatically put in use (depending on your card of course) making it unnecessary for the user to do much of anything besides initializing the module. The options that are usually off and can be turned on by editing configuration files, are usually still in testing; you can even say these options are turned off (and not disclosed) so as to avoid "harmful misuse" of the driver. Remember that this is a proprietary driver... they don't have to disclose everything about it if they don't want.