pageoneresults - 1:42 pm on Sep 3, 2008 (gmt 0) Maybe for Google but what about Yahoo!? How should I write my keywords?
The quick answer is no - words in meta keywords are highly unlikely to have any noticeable effect on performance, negative or otherwise.
Enter your keywords in order of importance, and be sure to use keywords that actually appear in your page content. Don't repeat keywords more than twice (and not consecutively!), separate your keywords with commas, and keep the list to under 256 characters.
Maybe for Google but what about Yahoo!?
How should I write my keywords?