Update on the nailbiting:
It's been 250 days and I still haven't gotten the habit under control, but I definitely see improvements in my nails and cuticles. What I ended up doing was installing the IFTTT DO Button app, which lets you put an icon on your Android homescreen which will add data to a beeminder goal. It's only 1 second less frictionless than an actual physical button I can press every time I bite my nails.
Further, I've set the nailbiting goal to autoratchet to 8 units before derailment, so I'm in some kind of constant danger. I'm considering decreasing this in the new year, and resolving to more regularly actually enter data. The IFTTT button sometimes fails and I don't always have my phone on me, but I've seen definite improvement with the threat of a $90 sting.