It all depends on what the broadcasters pick up on. If it's Brown's gag that the Tories' IHT policy was "dreamed up on the playing fields of Eton", then it will hardly reflect well on the PM. This clumsy, class-based politics didn't do Labour much good during the Crewe & Nantwich byelection, and it rather undermines Brown's frequent claim – frequently made in PMQs, that is – that he concentrates on politics, while Cameron concentrates on personality. Throw in Brown's G20 gaffe, and suddenly this PMQs session doesn't look all that rosy for him, after all.
If I were one of Brown's coterie, I'd be hoping that the broadcasters highlight his "The more he talks, the less he says" jibe against Cameron. As James said a couple of days ago, the Tories could still do much more to fill out their policy package, to present a positive front to voters. Attacks on that particular weakness may have greater traction.