In the preview messages there should be a spellcheck. It takes more time for the longer post to go through and check for spelling errors when if we had a spellcheck we could cut that time by a fraction. I think that this would also help for some users who do not know how to spell as good. That includes me.
I don't think we nead a spel chek... most of us kan spel just fnie! I thikn the real preoblem is that peoplw dont care aboue the quality of they're posts so they jsut type in whatevre their thinking asnd dont look to see if its right or not. Or else they dont know any better.
The use of apostrophes is a very, very widely misunderstood concept:
they're : means they are (if they don't stop they're going to crash)
their : means belonging to them (that is their company)
it's : means it is (I say it's about time we had some lunch)
its : means belonging to it (He found its reset button and pressed it)
An apostrophe is used to combine multiple words. The apostrophe shows ownership when it's attached to a noun, but not when it is attached to pronouns (they, me, etc). But you probably know this already.