The only way I'd really like to see a spell checker on this (or any other programming site) would be if it ignored anything between code segments. Otherwise, you'd have to scroll through countless "mispellings" to post it. Not to mention the longer the posted script (really, what spell checker is going to know $_ unless it's added manually?) the more time the server would take trying to parse supposed errors.
If it excluded code blocks, it'd be okay, though. I usually try to check myself during preview anyway.