From Mark Simonson's essay "The Scourge of Arial":
Arial is everywhere. If you don't know what it is, you don't use a modern personal computer. Arial is a font that is familiar to anyone who uses Microsoft products, whether on a PC or a Mac. It has spread like a virus through the typographic landscape and illustrates the pervasiveness of Microsoft's influence in the world.You can read the essay by clicking here.
Arial's ubiquity is not due to its beauty. It's actually rather homely. Not that homeliness is necessarily a bad thing for a typeface. With typefaces, character and history are just as important. Arial, however, has a rather dubious history and not much character. In fact, Arial is little more than a shameless impostor.