An old favorite from the TWoP FAQ:

One of the reasons I got so hooked on TWoP back in the day was because they didn’t take any crap.

Q: I love typing in all lowercase or all uppercase, ignoring proper grammar and punctuation, and writing my messages like I’m text-messaging on a cell phone with an eight-year-old. That’s cool, right? I mean, who cares? This is the internet!

A: Well, we care…but the sad truth is that other posters might skip over your posts if they’re too hard to read. Things like proper spacing, capitalization, and punctuation make your posts much easier on the eye, and they make you look like quite the Captain Smartypants, too.

Look, we’re not grading you. You won’t get banned for misspelling “definitely” or anything. Just try your best to write neat, coherent posts. Don’t type “2” for “to,” or “U” for “you,” or “l8r” or “LOLOLOL!!!!!!!!!!!” or any of that nonsense. Throw in a carriage return now and then to break up the text, and please use proper capitalization. Your computer comes with two shift keys. Use ’em.

Emphasis added by me. Link.