Can anyone shed any light on why pages would be flying on Google but not even getting a sniff on Yahoo?
I have had a series of projects live now and the pages are performing very well on google but don't seem to be even listed within Yahoo never mined ranking well. Any advise would be gratefully received..

I really don't have any advice. I just have an opinion.
The reason why more people use Google to find things on the net is because Google is great at placing content in front of searchers. It does not surprise me that you have pages indexed in Google and not Yahoo. I that happens to me also. IMO, that is ok, as long as your pages are indexed in Google you are already more than half way there. 65%+ of online searchers occur in the Google engine! So it is important to be there.

You should optimize your site for the Google Algo!

You can also, use Yahoos paid submissions to placed into the Yahoo directory. This could be very beneficial!