I'm assuming for this post that you're familiar with the 1993 Bill Murray vehicle (Go rent it right now if you haven't!), which I watched with my kids this past Feb. 2 for the first time in many years. I was struck in light of our recent episode on Plato's Gorgias on the evolution of the character as he's trapped in his ever-renewing limbo.
The obvious philosophical comparison to the movie is Nietzsche's idea of eternal recurrence, but it's nothing like that: in Nietzsche's picture, everything we do has extra weight, because it will happen again and again as history repeats, far in the future beyond our current experience. In the film, everything he does is undone, meaningless (apart from its effects on himself), lighter, and he can remember all of it. So it's actually the inverse of eternal recurrence.
Another comparison is Camus's "The Myth of Sisyphus," which is somewhat more apt. He finds that his ultimate happiness is in this woman who he has to re-woo from scratch every morning if he wants any kind of intimacy with her. But unlike Sisyphus, he can take a break whenever he wants from this task. In fact, each day is his own to choose what task to pursue.
The idea of starting from scratch is useful here, and points out some potential variations in the situation that would have really changed the dynamic. He starts out generally unliked, but still on civil terms with his co-workers, and in a position of fame and power such that he can easily impress others in the town who don't already know him. He has money, and, as time goes on, he has the advantage of intimate foreknowledge of the day's events. By comparison, if you've seen "The Wire," there's a picture presented there of a heroin addict who starts each day with nothing and is faced with the task of somehow acquiring enough cash to get his fix, and enough food to survive to the next day.
There's also an inconsistency in the film (and of course, given that it's just a light romantic comedy, it's arguable that the film doesn't owe us any consistency at all, so it's a wonder it works as any sort of philosophical example) in that any harm he causes to his body is undone the next day, yet he can acquire talents over his days, which surely also require physical changes beyond mere mental memory (which is of course really physical as well). Some of the other characters' reactions over time are also somewhat contrived, meaning they couldn't really be explained if they had total amnesia and were purely reacting to Murray's behavior that day.
Still, the picture of Murray's final (spell-breaking) day is telling: he effortlessly impresses everyone and does all the right things. How is he able to do this? Through knowledge. Knowledge of what's going to happen and of how people will react, but more than that, hard-won knowledge of how best to react to every situation. "Best?" Well, since the satisfactions of others' admiration of him are so short-lived, best in this case means the most satisfying to him. He ends up in a zen-like peace in the midst of his constant activity. He's figured out what battles he can't win (saving a dying hobo's life, actually seducing the one he loves), what difference he can make (even though presumably the damage to a boy falling out a tree would from his cursed vantage be eternally temporary), how to really make everyone around him feel great, and most of all, he's trained himself to behave morally. Even though he figures out early on how to successfully rob a bank and so be flush with cash for the rest of the day (and likewise, I'm sure there would be more violent and equally effective means to achieve this), this doesn't become part of his long-term routine, because he's already got enough.
On a different picture of human nature, he could have become a serial rapist, newly subjugating the town every day, but this, whether or not he explored such dark avenues in his many months of captivity, is not what ends up being satisfying. Given enough time to reflect on it, he (as any of us would, according to Plato's picture) seeks the good, and given enough acquired knowledge of himself, of social graces, of material circumstances, he's able to achieve the good unerringly. So this tale a counter to the "ring of Gyges" example brought up by Glaucon in The Republic. In that case, Glaucon says that man is fundamentally unjust, because if he had a ring of invisibility and could do injustice without consequence, he surely would. Groundhog Day is a demonstration that on the contrary, though someone with such power would try injustice, given the time to really sort himself out, he would turn to justice after all.