I ditched my smartphone for a (very)dumbphone a few months ago. The only thing I miss is the flashlight function.
[0] http://www.esato.com/gfx/news/img/2_2115i_lowres_2005_03_14....
I'm sure smartphones are good for a lot of people, but I haven't found the need for one personally. Anything I could do on a smartphone I can already do, I just have to wait until I'm in front of my computer. Which suites me fine.
Just set the background image to all white, touch any button and it will light up. Not too bright but usable in most cases.
The extended battery life is what clinched it for me. The funniest thing is that for years I would be way ahead of the curve and now I'm walking around with something that is probably more of a conversation piece than anything made by apple or htc.
"You use that?"
Calendar info can be synced with nearly all phones in other ways.
If you don't recieve important calls all that often, test yourself. Leave your smartphone at home for a week.
If you don't use it much while you're out and about, could you not simply have forgone it, planned your trip 5 minutes before you left home, and checked your email that evening?
I also don't like planning or sticking to plans when going out (how much fun is that anyway?). But I do like to get information on the go, for whatever I decide to do.