One other thing I have noticed (being European) is the moderate American reaction to any loved/respected figure announcing they belong to a sexuality other than straight. It usually goes something like: "Well, who cares what she does in her private life anyway" or, "Well she's still great". Both indicate a level of latent prejudice on a cultural, but not necessarily individual level.
In my opinion, bisexuality is not a legitimate sexual orientation; it is a half-measure for those too afraid to accept themselves as completely homosexual or a way for females to get attention.
That argument doesn't hold a lot of water. The fear of coming out as bisexual is the same as it is for coming out as homosexual. Your average bigot doesn't differentiate between the two. And contrary to how it may appear when you look at the number of female celebs choosing the "bisexual" label, they are both minority sexualities.
As for the original subject of this thread: you know what, I'm not surprised, but I am strangely delighted. There's a certain mild androgyny in her appearance that I've always admired, and I've always found the unashamed sexual honesty in her songs (White Houses springs to mind) incredibly refreshing - especially coming from a country where the media seems to believe that sexual acts are dirty and something to be ashamed of.
Go 'nessa