Nacho points out in What? No Google on Vista? Google Strikes Back on IE 7! at Search Engine Roundtable a screenshot showing how Google is not among the recommended search engines on a guide for those wanting to customize IE7. OK, the page is under construction, but it's hard to believe it's an oversight. Below this, he's got a screenshot showing how Google is prompting in IE7 for users to make it the default search engine.
I seem to recall seeing something similar like this from Yahoo, but I can't track that down. It's all kind of an aside to me. I'm not leaving Firefox!
Postscript: Just remembered the Yahoo thing. It's how they try to promote you searching from Yahoo rather than Google in Firefox's built-in toolbar: