Onebox results really can be quite dominant. Look at this screen grab of search results for Toby Dawson. Hard luck to you if you have a content rich web site about the Olympics and were hoping to enjoy a traffic boost. Hard luck if you'd rather, say, have a hotline to the BBC's advert free website instead of NBC. Well done if you happen to be NBC though!
Of course, I'm writing this with my SEO hat on. There's a good argument in favour of the user experience. I'm not a sports fan (I'm a search engine geek) but even I can see how Google is quickly delivering the best possible match for my search.
Could this use of the onebox be a foreshadow of how Google Base content could interact with the SERPs? It's a valid question, one that's easy to speculate on but impossible to answer. Google tends to try these things to see if they work and then keep or drop them as the trial suggests.