So long as Google only returns these sponsored ads for searches for the company name, I don't see this as being a problem at all, given the fact that many users are using the address bar integrated search in place of bookmarking or typing URLs.
Where this would become a problem is if they start expanding this to searches beyond simply the company name, and I think there is a bit of a gray area there. As someone else pointed out in this thread, showing the Southwest banner in response to a search for "cheap airfare" pretty unambiguously crosses a line, but what abut something like "book southwest airlines flights." One could argue that the user was attempting to get to the southwest airlines website to book a flight, so showing the Southwest banner would be appropriate, however, companies like Expedia, Kayak, and so on, whose links would now be much further down the page, would likely disagree.