See what I mean about it being a common reactionary rant?
Everybody starts off with the "kids these days can't add up" speech yet nobody can answer your question and point to reseach indicating issues with mental development linked to calculators.
In fact the Flynn effect
http://en.wikipedia.org/wiki/Flynn_effect
has shown a rise in average IQ of about 3 percent per decade.
As the use of calculators became standard practice in the Early 80's and this did not slow the Flynn effect it would suggest that it is absolutly untrue.
It seems kids were dumber in my day!