I think that upgrade is projected to come out sometime in the fall.

There are some reviews out there about a Preview image floating around. But I'm sure that preview has to be so buggy that it won't have quite the same performance as the completed OS that'll be released. I'll adjust my excitement based on those reviews of the final release.

The UI looks interesting. But if it wasn't free I don't know if I'd pay the extra fee just to use it.