Many people do write how they speak, which results in would of and prolly showing up in formal writing. I take written mistakes much more seriously than spoken mistakes. We say things like kinda, nah, and gonna, and that’s totally fine, but those words are never acceptable when it comes to a research paper or a resume. Never, ever acceptable. Here’s what I say: colloquialism is fine in everyday conversations with your buddies, family, and co-workers, but is unacceptable in the majority of writing and in conversations with superiors. Just because you say it a certain way doesn’t mean you have to write it that way.