To be clear, all the statistics you cite say simply that "the majority of the US citizenry" drink coffee. Not that they experience unpleasant side-effects.
For those who don't experience unpleasant side-effects, the cognitive-enhancements, learning-improvements, Alzheimer's, Parkinson's and dementia risk-lowering, depression-lowering, and cancer-fighting effects (most citations here) make it extremely attractive -- at least until we have tDCS cafe's everywhere.
I've been extremely curious, but a little too risk-adverse to start dabbling in DIY-tDCS. Having a 14-month-old daughter at home makes the prospect of accidentally frying my brain less attractive. But, as I said, I'm extremely curious and cautiously excited, and when the field matures a little more I'll be right there.