Spelling!

Spelling mistakes bother me the most in sites that are trying to sell me something as if they can't spend time checking their grammar, how am I supposed to trust that they take care with my order?

As for blogs and smaller sites, as long as it's not frequent in the article I usually just ignore them or point them out via the comments as long as I can still understand the typo. The usage of the wrong word is another common mistake but that one is more forgivable as spell checkers can't verify that.