=)
Anyway.....I agree that a lot of it depends on where you ski.  Fat skis are not neccesay on the east coast.  On the west coast, it is a completely different story.
I skied skis in the 90-95mm waist when I used to ski in CO.  No reason to ever go thinner as they could do everything.  You really don't need them to be fatter, but until you have skied on a 110+ waisted ski or a reverse sidecut ski, you really can't say anything.  These skis absolutely kill skinny skis on any sort of soft snow, not just deep powder.  That is what people often forget.....
One of the best snow conditions for skis like Spats, Toons, the lotus 138, etc, is when it is heavier, windblown snow only 3-6" deep.  They just kill it in those conditions.  Normal skis just cannot compare.
As you get even further west (CO, OR, WA, and BC) I think fat skis are even more important.  The snow is much heavier out here and float becomes extremely important.  When I first got to WA, my everyday CO skis were just too fucking thin and small (179cm Seth Pistols).  They just didnt float enough and were not long enough to bust through the now heavier chopped up snow.  Now I pretty much ski a 190cm long 118 waisted ski everyday.  I have no issues on groomers and it allows me to ski anything I want.  I may not be able to rip groomers as well as the 95-waisted ski....but I can ski what matters to me much better.
I think now I plan on going to a 191cm 140/113/128 full twin as an everyday ski, then make a reverse camber ski for powder days.
I do believe there is a limit to how fat you can go.  The euro company Durets (?) who just made a pair of skis that was 170mm in the waist (the exact same size as a monoski they make...they just maded two pairs and called them skis...) is ridiculous.  I cam see, though, were skis such as the Kingswood midfat (at 146mm in the waist) would be an awesome ski to be on.  You would need deep snow for something that fat, but there are people who get to ski snow like that on occation.
What everyone needs to remember is most of the people buying these uber fat skis are doing so as part of a quiver.  Most people who own spats do not ski them everyday.