Because I can say this: .Mac is really cool. It supports 1 to many authentication to .Mac accounts. The publisher needs a .Mac account, but "subscribers" do not need any .Mac account! This enables all sort of groupware applications via the .Mac framework!
They said the scale is not great, but for applications with lets say 100 subscribers it would work great. Like sharing your photos with family and friends a la Flickr - I'm expecting the next iPhoto to support this.
The developer preview of the 2.0 .Mac framework will be available for download early July (They said the 1st)
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