I find when the line shoots across (which it does repeatedly & regularly) that this changes the browser behaviour in both Opera & Chrome. It seems to stop the spell checker in its tracks, often when you're mid check, plus it removes any line breaks in the text editor.
You end up having to re spell check several times, often having to type more to get the spell checker active again, and repeatedly re-enter line breaks (eight or nine times writing this short post). When the site is in any way slow, it's unusable.
However, from a usability point of view it is very poor all the time and you should remove it if you cant alter the behaviour, as no doubt it will put lots of people off. I certainly post less, as it's hugely frustrating.