One thing to keep in mind if you did pay for Ad Free seems that spelling cow is inserting their own advertisement code into your forum.

Apparently, from what I was able to find out, the service is ad free for the first 30 days. After that, you can still continue to use it, but as soon as you place a check into the spellcheck box, a small ad will display below the post screen. Uncheck the box after you are finished using it, and the ad goes away.
I suggest not to check the "Spell Check As I Type" box until after you are finished inserting your post. Then check off the box, correct any mistakes, and uncheck the box again.

Best we have until a better spellcheck system can be found.