Despite Bing's steady gains in search query share since launch, they don't seem to be capturing the hearts of advertisers. From speaking with advertisers, the problem seems to be AdCenter, which is frustrating on many levels for those with bucks to spend.
Additionally, the dip in ads for Yahoo! should be concerning for Microsoft as it will seek to begin implementing the search deal with the Sunnyvale company this year.
There is a silver lining for Bing and Yahoo! when they collaborate. Advertisers do tend to love the ROI they see on Bing. They just need to get share and search ad tech in place to make advertisers happy.