To some people, it's not much better than "pen and paper", but I find org-mode in Emacs very handy. And yes, I've got it on my smartphone. I've not played with the Android or iPhone org-mode apps, but org-mode keeps everything in plain text, the tables export to CSV and TSV, plus there is already quick and dirty graphing built-in (org-plot/gnuplot).
As for more advanced stuff, I've started looking into statistically analyzing the data, also in org: http://orgmode.org/worg/org-contrib/babel/intro.html