HI Play
For the record, if there is a duplicate content issue on any of the major SEs (Google, Yahoo, Bing (Nee MSN)) a site would only be demoted in the SERPS if it was a duplicate of another site (or close to it) – not because of a few singular lines of text.
You would not have lost a #1 spot on any of the SEs because a few lines of text had been copied into a blog post. It just doesn’t happen.
Also as your site had the original text, it would not have been penalised. If any site had been punished it would have been the site that had copied your text.
I am not sure why your site would have been penalised by Yahoo, but to blame it on something this trivial really (with all due respect) shows a lack of understanding of how search engines rank sites.
Check with other SEOs and you will be assured that I am telling you the truth.
Regards
Simon