I think the quality of Stack Overflow questions and answers is, in general, better than the web results for the same queries returned by search engines. So, personally I'd always like to see if Stack Overflow (or any Stack Exchange site for that matter) has something related to what I'm looking for on Google.
But, I don't want to just search on Stack Exchange sites, so I still want to search on Google first, it's just that I want to see Stack results on first page, even if Google doesn't think they are more appropriate. May be something like Google Subscribed links?