This is from MacInTouch
I don't know how valid that concern is but I thought I'd let you guys know.
This is in response to Howard Stollery's comments about using an extended desktop with an iMac G5:
The Screen Spanning Doctor program he is using as been around for quite awhile. What it does it modifies Open Firmware to allow these machines that only supported mirroring (any white iBook I believe) to have an extended desktop. So the limitation is not due to the OS, but it is the default in the Open Firmware settings. Once you reset that, you would need to apply the patch again.
While likely not a major issue for an iMac G5, I believe that the extended desktop was disabled in the iBooks for good reason (even though the graphics card is more than capable). iBooks rely mostly on convection through the keyboard to disapate heat. In my experience, the keyboards especially on the left hand side get warmer than they do in a Powerbook. Remember, that metal casing of the Powerbook is really a big heat sink. iBooks don't have that luxery. And while many Powerbook owners complain about fans always being on, they always seem to be off with iBooks unless they really get hot. So what happens when you close the lid on an iBook with this hack applied? Likely, you will get a ruined LCD display. While I have not seen the effects personally, my IT support staff has. Also, you are eliminating one of the primary ways an iBook gets rid of heat.
While it is probably okay to apply the patch and never close the lid and use the setup as two desktops, I really can't recommend using something that hacks your default hardware settings. There has been discussion that apply this patch can void your Apple warrenty/Applecare policy since you are now using the hardware outside of their specifications (I bet this applies to the iMac G5 too).
Given the numerous reports I see posted on the net and feedback I get from our IT staff, it seems like there is not much wiggle room when it comes to Apple deciding that a machine has been abused. Certainly hacking your hardware seems like you are opening a can of worms. What do you do if you machine won't boot and you can't restore Open Firmware to the default settings before sending it off to Apple.
I don't know how valid that concern is but I thought I'd let you guys know.