I was one of the people who hadn't given Blaise much thought at all, though I found the various fanon Blaises interesting. And then JKR described him, I went, "huh, he actually sounds really hot," and then merrily continued with caring only about Draco and, to a lesser degree, Harry (that's just in the books, though -- in fandom I really like to read thoughts and essays and suchlike about all the characters).

And then I was astonished (and disappointed, and then sad when I realized that I probably shouldn't be so surprised) when finding out that Blaise was black upset some people and made them less interested in him. Though luckily no one on my flist reacted that way.