Yes and no.
I think the grammar should be as good as is necessary to understand what is being said and as is necessary to sound like a reasonably intelligent human being for whom english is his/her first language.
On the other hand, if one has to worry too much about his grammar being perfect, it is sometimes harder to fully express oneself. I think there is a certain level/type of grammar error that is acceptable in a post that would not be acceptable in an academic work, etc. Something along the lines of poetic license.
And yes, that last sentence was meant to be an example. 🙂