I love fat skis, and have been skiing 121mm waisted Liberty Double Helix as my inbounds daily driver (only ski) for years now. They are great fun and ski groomers and hard snow really well. Before you jump all over me, please note that I got into skiing via the backcountry, and for years have only skied on powder or soft snow days.
My life has changed, however, as I have two kids who can only ski on weekends, no mo matter the conditions, and frankly conditions here in Montana are getting worse. It doesn't stay as cold after a snowstorm as it used to, so the snow gets warm and then sets up harder than it used to. I still enjoy the DH on firm groomers, but on very steep double blacks and the off-piste terrain I usually choose they aren't fun when the snow is really firm.
And, my knees are wearing out. Combine the fact that I'm skiing more hard snow conditions than ever with my knees and I'm going skinnier this year. Just picked up a Fischer Motive 95ti to use as my daily driver and travel ski. Is it still too fat for many of you? Yes, but if it is boilerplate I won't be skiing (at least inbounds if there is any soft snow in the bc). I'm excited to give them a try, but would really love to have a ski 105-110 for my daily driver as I think I could happily use that as a one ski quiver. I'll live with these, though, as evidence is strong (http://www.montanakaimin.com/news/article_b73f0f3a-b0ba-11e4-9f66-fb3b2e4b192c.html) that staying below 100, and even better under 90, is better for your knees on firm snow.
Years ago someone gave me a pair of K2 AK Launchers (don't know the dimensions) and I mounted them up with tele bindings. People in lift lines would ask me if they were water skis. I used them as a novelty until one day I bounced down a mellow slope with 4" or so of powder, and all of my buddies on skinnier skis face planted. I was shocked until one of them asked me "how did you ski that breakable crust so easily?" The answer was I floated on top of it and hadn't felt it at all. That was when I first appreciated fat skis, and since I have had many days of 4-6" on top of icy crust where I am skiing the soft snow instead of the crap underneath. Fat skis are not just for deep days, as they can make small snow storms ski like big dumps. No, they aren't perfect everyday, but depending on your bias, they can be very fun.
If I were ripping firm groomers all day all the time, I would buy something skinnier.