Microsoft may or may not be involved with antitrust complaints against Google in Europe, related to Google+. Pretty vague, I know, but conflicting reports are painting it that way.
Reuters first reported: "Microsoft and several other companies have complained to EU antitrust regulators about Google's social networking tool," and that, "The complaints, which have not yet been filed formally with the Commission, may prompt the European Commission to broaden its ongoing investigation into Google, which focuses on whether it is too dominant in the web-search market."
Reuters cites "people familiar with the matter".
ZDNet has countered the Reuters report, indicating that Microsoft is "not involved in an antitrust complaint over Google+." Reporter Mary Jo Foley cites a Microsoft spokesperson as saying, "We have not filed a complaint regarding Google+."
Still, as you can see from the first Reuters quote above, it says that complaints "have not yet been filed," so that doesn't necessarily mean the report was false. Furthermore, that Reuters article also quotes a Microsoft spokesman as saying that the company had not filed a complaint.
So, it seems clear that no complaint has been filed, but apparently it's still possible that formal complaints are in the works. I guess we'll see if it happens.
Foley, while noting that Microsoft has sought other regulatory intervention against Google implies that Microsoft doesn't have much of a vested interest in intervening against Google+, but Search Plus Your World could give Google an advantage to Google as a search engine, in terms of delivering personalized content to Google+ users. I'm not sure they would have much of a leg to stand on, however, since Bing has Facebook and Twitter data at its disposal.
Also, let's not forget that Microsoft is part of the FairSearch Coalition, which aims to inspire regulatory intervention against Google at just about every turn. And what do you know? They just opened up shop in Europe.