...as I said in another place: unless and until they can bring themselves to drop paid inclusion (you know, charging US to scrape OUR content)...Yahoo Search will never see a reversal of the current trend.
Imho, products grow by leveraging people...who tell others...who have a good experience, who like what they get, etc.
I've personally ensured over 1,000 people that I talked to about search both understood the ramifications of paid inclusion AND saw their head nodding in agreement that it's truly an "evil program".
From rumors (or a press releas?) Google's half a million AdSense publsihers all know about paid inclusion, if they are at all well informed...if each of thse people tell 10 people, that's 5 million people actively campaigning *against* Yahoo Search.
It might not seem like a lot but we've all seen what is happening with Twitter, based on marketer's ability to leverage the platform for communication...everybody is loving it & sharing, b/c they find value. Zero people that I've met in the last 5 years would do anything close to the same for Yahoo.