Just to be clear: The European Union isn't making noise about holding up or investigating Microsoft and Yahoo's proposed search partnership (at least not yet).
Reuters reported on September 15 that the European Union antitrust regulators are in "informal talks" with Microsoft and Yahoo regarding their search deal, via which most of Yahoo's search would be powered by Microsoft Bing. I've seen a few folks jumping to conclusions about what this means -- which isn't too surprising, given the European Commission's proclivity toward coming down hard on Microsoft around anything that it deems stifling competition.
The U.S. Department of Justice, for its part, has requested more information on the proposed Microsoft-Yahoo deal.
It was a bit unclear in July, when Microsoft and Yahoo unveiled their proposed search deal, whether the EU would require official notice, and, if not, how and where notice of the proposed deal would need to be filed.
A Microsoft spokesperson had this to say about the Reuters report:
"We said when the agreement was announced in late July that it would require clearance in the US and Europe to proceed, and that additionally, we would be filing for clearance in Korea, Taiwan and Brazil."
Microsoft has notified the EU as it said it would, he added.
Update: I misused the word "notified" here without realizing the legal ramifications. Microsoft has informed the EC of the agreement and engaged in informal discussions, but has not officially "notified" them, given that Microsoft is still determining whether official "notification" is required.