Apparently there is a study around that people actually prefer Bing's results to Google's if you swap the layout (i.e. show Bing's results on a Google page and vice versa). That may just show that Google has the better brand, but Bing's search results are apparently not that bad.
(I don't use Bing and have no conceivable stake in this fight.)
Your "source" is that blog post from the other day by the guy who worked on Bing three years ago, no? His "source" was an "internal study" that he provided no links to. Just sayin'.
I must honestly say that I forgot where I got this from, which is not a good thing. Thanks for pointing this out.
That said,
http://mashable.com/2009/06/07/blindsearch/ (apparently based on http://delicategeniusblog.com/?p=839) suggests that in a blind three-way test in 2009 both Yahoo's and Bing's results got picked as the best regularly (Google gets 41%, which is a substantial but not overwhelming advantage.) Note that that guy works for Microsoft, too.
(I don't use Bing and have no conceivable stake in this fight.)