What does Conan O'Brien have in common with the combustible, out-of-control train from the Fox action thriller Unstoppable? Not much, I'd say, but the studio and TBS have linked the two anyway in a commercial that's airing this week on O'Brien's new late-night chat show, Conan. "Go from 190 pounds of talk-show host," the ad says in bold type, with no voiceover or dialogue, "to 1,000,000 tons of steel." Get it? Neither do I. If the spot means to say that both are, well, unstoppable, then I could grasp the idea. O'Brien has risen from the ashes of a failed stint on The Tonight Show, and he's more popular than ever. But (no real spoiler here) the train in the movie, opening Friday, actually is stoppable. (That's what our heroes, Denzel Washington and Chris Pine, will spend two tense hours doing.) The growing trend of mingling TV-show content and advertising, so that viewers are less likely to fast-forward through the breaks, is working in some cases. It's even engaging when it's cleverly done, like the recent zombie-themed Toyota Corolla commercial that aired during AMC's The Walking Dead. But anything that can be copied can be copied poorly. Sorry, Coco, I'm all for seeing you plastered across every available piece of TBS media, but stop it with the Unstoppable crossovers.