Speaking only for myself...
I'm a very calendar-oriented person. My birthday and New Year's are my two favorite events. Even though it's only a one-day difference, I used to get really excited about the shiny new year in which I was perfect...so far.
Of course, the inevitable disappointment would eventually find me.
(Just to clarify: I still love New Year's, but I'm much happier now, so I don't have as much of a need or desire to put the old year to bed.)
That having been said, one way I knew that this time was different touches exactly on your point, I think. I was going to start a new eating plan on January 1, 2009; however, on December 29, 2008, instead of eating everything in sight for three days, I decided that It Was Time and I Was Ready. And it was, and I was!
Some people, like you, get an internal "I'm ready" signal--I guess some people use the calendar as an external push.