Tom Parish, whose blog I edit, sent me the article below. He hired me because he fully believes that spelling counts, that website owners have a tiny amount of time in which to make a good impression, and they don't need to make their readers decipher spelling errors.
I agree. I'm no stickler for "formal" writing in blogs, websites or Podcast show notes, however. There are lots of versions of English - ranging from casual to legal - and I'm fine with casual writing in a casual setting. What I am a stickler for, no matter the setting, is correct spelling and grammar. Casual writing is not improved by misspelled words and poor grammar. It just becomes sloppy, and the writer looks like he/she doesn't care about you, the reader.
So, IMHO, spelling definitely counts.