That is to say a dual layed, double sided DVD (DVD-9 on both sides).  A comparison would be movies with full screen on 1 side; WS on the other.  Any games utilize this? 

Nope. They are all DVD9.

That's too bad. The dev companies could lower royalty costs. Though scratching would become double the problem (360 install feature to compensate, maybe?)

I guess it would also depend on whether the range of drives used in 360 consoles could handle that format. Are those discs supported by all DVD drives?

Maybe cost is a factor too, if 1 of those discs costs more than 2 DVD9s, plus MS use a particular structure for their discs that only actually leaves around 7.3GB of space for a game. Perhaps that would also be affected if those discs were used? There has to be some logical reason otherwise they could double the space easily.

I HATE DVD-18 DISCS. They are horrid and nearly impossible to handle. I always touch the top layer putting them back in the case and smudge them unless i am paying careful attention.

You'd still have to get up and turn it over though... the 360 only has 1 laser. tbh I would prefer 2 discs, all it does is possibly cut costs for devs. (I say possibly because for all I know it may be more expensive to press on both sides than on seperate discs)

360 does not and will never play DVD18 games. Why? - to put it simply 2 DVD9's is about the same cost (give or take a cent or two) and DVD18's scratch too easily...

Not to mention multi-disks games = more money for M$ due to higher royalties ...

I wonder if DVD quad layer is possible? That would give 18gb on one disc on one side?

If you did this, you would have to release all new players, as todays would not read them. It would also cost a lot more.

The biggest problem with that, is in the end you have an all new format that only suppots 18 gig. Why would you want to do that when you have a current, and suppoted, format that supports 50 gig? (and 200 gig in testing).

I would prefer two have two discs rather than a double sided one, partially because the presentation is better, but mostly because I wont be as worried about scratching