A good friend of mine just signed my high school year book joking that he should of won the chess club presidency. I've seen this grammatical mistake many times during my high school career - as an editor of my school newspaper, I had to correct dozens of these errors from bright, intelligent young reporters - and it seems to be pervading the writing style of the newer generations. This alteration, arising because could've, would've, and should've are pronounced exactly like could of, would of, and should of, is actually by no means a recent occurrence, first showing up all the way back in 1814. It was used in an 1854 letter by renowned writer Charlotte Brontë, and countless others through history. However, now it seems much more common than before, due partially to propagation by the Internet, and many years down the road that spelling could quite possibly take over as prescriptivist grammar Nazis die out and nobody's around to correct it anymore. It's actually a pretty curious snapshot into linguistic development in action, and fun to observe from a pragmatic perspective. The phonological reason for the f and v confusion is that both letters are labiodental frictatives, which means that the lower lip is raised to the upper front teeth and air is forced through the mouth to make the sounds. The only difference between the two is that pronunciation of v includes vibration of the vocal cords, but otherwise they're the only two consonants in that category, so they're easy to confuse. Clearly, the alteration won't be disappearing anytime soon.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.