Sketchbook on Windows 8 Consumer Preview: Worry about WinRT

I have Windows 8 Consumer Preview installed on my EeeSlate, and so far it works pretty OK.  And thanks to this post, I even got my bluetooth keyboard and mouse working.  There's one thing, though, that troubles me: SketchBook Experss Metro app.  I tried it and found that the experience of using it extremely sluggish, especially when using zoom.  This is odd, because I have SketchBook Pro 2010 running on the desktop side and it worked pretty OK (it has a bit stylus precision problem but that's yet another story).  That makes me very worry about how effective can WinRT provide as a runtime platform.