I use the Oxford comma wherever its omission could lead to an alternate reading, and omit it otherwise. You know where people run into trouble? Where their omission or inclusion of the Oxford comma is a point of principle, rather than a decision dependent entirely on content, context, and sense.
People who always omit it risk giving the reader two grammatically valid ways to read the statement. In contracts or in law, this can be fatal.
People who always include it run no risks in terms of the sense they wish to convey. But in using a comma where none is needed - where no alternate reading could arise from its omission - they risk seeming rule-bound, precious, given to stylistic affectations that serve no purpose. Adherent to a principle, without having any feel for its actual use or effect.
The Oxford comma, like every mark of punctuation, is a tool to direct meaning along the writer's desired path. Clarity demands its use where necessary. Elegance and simplicity would seduce us to omit it where its presence adds nothing. There are those who love and some who hate the Oxford comma, but the majority who simply omit it without thought do so out of an instinct for simplicity, and a dislike for needless flourish or ornament.
But we can't lose sight of the controversy! Gratuitous use of the Oxford comma (where its omission could not possibly introduce ambiguity) DOES add something! It signals to the world "I'm Team Oxford Comma!" With all that that implies, and most of what it implies is good. I'm not Team Oxford Comma, but most of those people are pretty funny and great, and it's sweet and wonderful that so tiny a mark could say so much. An Aldis-lamp flash to the like-minded resistance.
The Oxford comma will never die. It will keep barging in where it's not needed, pointing proudly to where it sometimes is. And its opponents will omit it scrupulously, sometimes to the detriment of their case in court, more often to the hilarity of readers who spot the wild ambiguity unleashed. The Oxford comma is the only thing that can leash that beast. Do we need it? Yes.
Do we need it all over the place? Probably not. But you ought to admit, it's a little bit cute.