I generally don't comment on people's online use of any language, because I don't know the real reason why they may have misused the language. If it is hard for me to read I don't read it, I don't comment, and I just leave it alone.
The people that are more concerned about pointing out the quality of online posts as opposed to the content of the post have earned an online nickname that I don't feel comfortable posting here. Some of you may know it and may be guilty of it.
There are two ways to tell someone about their language mistake, a nice way and a mean way. You can nicely point out an improper spelling and suggest a correction, or you can point it out, make a rude comment on it and behave all high and mighty.
Either way, in a format that is purely text based, it is difficult to attain the correct attitude of a post and whether or not someone is being helpful or mean. You can read anything in a happy, sad, mean or angry way in your head, but you can't really know if that was the intended way for the message to be interpreted.