I almost forgot to check my bandwidth for December — and it shows. Unfortunately, vnstat only keeps the daily stats for the last 30 days, so the daily stats for the beginning of December are lost:
However, the total stats for the month are stored: 20,391MB down, 6,449MB up, 26,841MB total. I'm not sure what accounts for the spike in activity on the 30th, but the 31st may have been caused by us watching the Times Square festivities on the internet (which for some reason had a lesser effect than whatever happened the day before).
Worthy of note this month is that I've started watching the online web series The Guild in high-definition on Xbox Live. Although HD, they are short, less than 10 minutes each, so the file size each is only a couple hundred Megabytes apiece, about once a week.
Totals are down about 700MB from last month, with December showing the lowest usage since I started monitoring.