Its about same for us. I have been trying learning about the difference in shoppers on the big 3. Conversion is so much better on Google, but people must search Bing and Yahoo looking to buy.
conversion rate is always base on visitors flow. we can't predict it but we can make good conversion by giving new offers.
The conversion rate as it relates to a website is the number of web users who complete a specific action upon arriving at the website. Your conversion rate refers to the percentage of visitors to your website who respond to a distinctive call to action. The conversion rate is usually given as a percentage. You can figure out the website’s conversion rate by dividing the number of users who complete the predetermined action by the total number of individuals who visit the web page. The higher the percentage is, the greater the conversion rate that occurs.
From my past experience campaigns ran with bing didn't preform as well as YSM when speaking in terms of ROI.