Around mid-December I did a
redesign of my blog (actually I chose a different template and tweaked it a little bit :D) and forgot to include the Google Analytics tracking code in the new template. The result was that according to statistics I had 0 visitors in late December - early January. First I thought that this was because of the holiday seasons. The moment I became suspicious was when people started adding comments (so there was clearly activity on my site) and the statistics still said that no one looked at it. So I checked it out, and sure enough the tracking code was missing. I included it again, and now everything is fine.
A tip: if you want to get the tracking code for a certain site in Google Analytics (because you're in a similar situation), go to Google Analytics, click on edit for the account and go to Check Status (it is a small link in the upper right corner of the table). You will find your tracking code there.