Besides a pre-merger investigation by the Federal Trade Commission and a newly confirmed review by the European Commission, the Senate Judiciary Committee's antitrust panel is now planning to hold a hearing on the acquisition in September and so is a House Commerce subcommittee on consumer protection worried about privacy.

Google expects the deal to close by the end of the year, but - while Congress has no authority over mergers - the additional probes could push that date out, not to mention give critics of the deal - like Microsoft, AT&T and Yahoo - a public forum to voice their concerns and put pressure on the FTC, which has generally been reluctant to mess with emerging technologies.

Meanwhile, Europe's privacy watchdog, the Article 29 Data Protection Working Party, has yet to decide whether Google's offer to cut the time it holds personal data like preferences to two years is enough.