PHIL: Today is tomorrow. It happened. You're here; I'm here.
RITA: Why weren't you like this last night?
PHIL: It was the end of a very long day."
The end of Groundhog Day shows us that Phil Connors has finally succeeded in escaping from the seemingly endless repetition of February 2nd. We realize that his escape has been triggered by his transformation into a good person and by the fact that he is finally worthy of Rita's love.
It took him nearly a decade ("a very long day"), but he has finally succeeded in being a good person. The movie wraps up with a nice moral for all of us, which goes something like this: all of your days will feel empty and meaningless until you learn to be kind to others. You might find it a bit preachy, but oh well. It preaches something pretty dang awesome and heart-warming... if you ain't a bit misty-eyed by the end of this movie, you're probably a robot.