Yahoo! will not ban you if you have keywords in your meta keywords tag that do not match the exact content on your page. I mean, if you have meta keywords that are totally off topic to the page, and someone reviews the page, it might raise a flag. But if you have a page on plasma TVs and you do not use the word Ã¢â‚¬Å“televisionÃ¢â‚¬Â on the page copy, but you use TV and then in the meta keywords you decide to add Ã¢â‚¬Å“television", how can that be bad? Of course you may want to add any keywords that are important to you to the visible page copy, but if you donÃ¢â‚¬â„¢t, I donÃ¢â‚¬â„¢t think it will cause a penalty. You just wonÃ¢â‚¬â„¢t rank that well for the keyword, since its not in your visible page copy.