The somewhat debatable origin of the fountain pen can be traced back to Walter Sheaffer in 1907. He's the one that's credited with perfecting a pen that sucked up ink through the tip, in place of reloading the pen with ink with a cumbersome eyedropper. This made the fountain pen vastly neater than older-style pens1.
Nonetheless, there's something very sensual about writing with a pen that uses liquid ink. Indeed, when writing with a fountain pen, the nib seems to positively glide across the page with such effortless grace as to make the physical act of writing a joy. These days, if you prefer, you can buy plastic cartridges for a fountain pen. These little fellows practically eliminate any chance of a mess2.
In this era of mass production, a $100-plus writing instrument might well seem an extravagance. Yet a good fountain pen will last a lifetime. It lends character to the signature of its user, and makes writing a much more thoughtful experience.