The Wall Street Journal has a "people familiar with..." story up about the Federal Trade Commission's antitrust investigation of Google and there appear to be three main lines of inquiry:
Six weeks after serving Google with broad subpoenas, FTC lawyers, in conjunction with several state attorneys general, have been asking whether Google prevents smartphone manufacturers that use its Android operating system from using competitors' services, these people said.
They also have inquired whether Google grants preferential placement on its website to its own products, such as Google's "Places" business listings, its "Shopping results" or Google Finance services above most other results.
And they're looking into allegations that Google unfairly takes information collected by rivals, such as reviews of local businesses, to use on its own specialized site and then demotes the rivals' services in its search results, the people said.
-WSJ, August 10, 2011
UPDATE: The Journal filled out the story a bit more later. The Android complaint is based on mobile location service Skyhook's lawsuit filed last year. That's the one where a Google exec said they could use the Android compatibility requirement as "a club" to make phone manufacturers get in line.