Here's the Obama ad:
The Washington Post's "The Fact Checker," interestingly, took a pass on rating that ad but noted that a previous similarly themed ad had earned Four Pinocchios. At issue: While Bain Capital may have been a big outsourcer, Mitt Romney wasn't in control of the company at that point.
So the Post, along with a separate analysis from Factcheck.org, becomes the basis for a Romney campaign ad. The ad doesn't say directly: "Obama is a liar." But it does say he "doesn't tell the truth." And that "candidate Obama lied about Hillary Clinton" -- at which point then-candidate Clinton makes a special guest appearance in the ad declaring "SHAME ON YOU BARACK OBAMA."
Of course, none of this is to imply that the Romney campaign is a paragon of truth. Here's The Fact Checker giving Team Romney Four Pinnochios. Overall, both candidates are in a tight race for long noses.