I find Yahoo loves links, in a different way to Google.
Yahoo will count links from anywhere these days, similar to the old MSN ways.
If you do a lot of cross linking within your site, Yahoo lovs it. So yes, copy is important as with any search engine, but good copy and good internal cross linking will get you there for yahoo.
With Google, the links need to be better quality.
I too get good conversion rates in some sectors on Yahoo, but the quantity just is not there.
Will more people use Yahoo now that Google are showing their ads in Yahoo?
This is in testing and unless more people know about it then I guess nothing will change.
Would people switch to Yahoo just because of Google ads?
Looks like these questions are for a whole new thread and different topic.