Romney's margin of victory in Ames is not overly impressive -- given that he's outspent all the other participating candidates combined by a four-to-one margin in the Presidential campaign to date -- but it's solid enough. The breakout moment is Huckabee's, as he pulled out a solid second place; he now needs to seize the moment to get some momentum, and money, and media attention. He has a chance now to become the Bill Richardson of the GOP side: certainly not top-tier, but legitimately part of the picture.
The rest are toast. Brownback's third-place finish might not be enough to keep him around much longer. Tancredo's fourth is a serious blow, although it's possible he could hang around for a while, raising money from the immigrant-bashers. Paul is a different story: fifth place is enough for him to keep getting attention and gaining spoiler status. Tommy Thompson is now officially done, and Duncan Hunter already was done -- I doubt either of them will even be in the scheduled post-Labor-Day debate.
You have to hand it to Romney. Entering the year, there was nothing that suggested him as a more viable candidate than Huckabee, Brownback, or T. Thompson. Today, he is clearly in a different league than them, and it's all because of his political skill at marketing himself.