Being an East-Coaster, I don't get a chance to ski deep snow very often. I have tried a couple "fatter" skis (waist widths in the 80+ range though); I've never found them to be "magic wands" that suddenly make difficult conditions easy though.
Maybe my natural stance doesn't co-operate well with wide skis? I do naturally stand with my legs fairly close, so I feel on fat skis that I have to fight my natural stance, and it just doesn't work for me.
My "fat skis" are a pair of K2 Recon's (78mm underfoot). They do smooth the ride out somewhat, and there are time I've definitely been glad I've had them under my feet (boot-top deep chowder in Highlands Bowl, for instance). I have no desire to go any wider then that.
But, for instance, I've skied knee-deep fluff at Stowe on Elan Speedwave's (69mm underfoot), and was never wishing I had my Recon's. They worked just fine. Go fast enough and everything floats.
And I've been in some "snow" that resembled Elmer's Glue where my technique was so god-awful that I would have been eating snow no matter what was under my feet.
Anyway... I guess my point is that, for me at least -- in conditions where I feel confident, I don't think going wide would buy me anything. In conditions where I'm semi-confident -- there's some assistance, but I think the "assistance" is a long way from "magic"... More like, "well, I know I can get out of this without killing myself". And in "dear God, please get me out alive" conditions -- well, I would suck in those conditions regardless of what's under my feet (as I've discovered several times).