At the PDC, developers could try it out in the hands on labs. On Channel 9 last year, you could see demos. Now, you can download its first CTP (Customer Tech Preview) and check out a new Channel 9 video.
I'm fantastically excited to see the first CTP of Expression Interactive Designer, "Sparkle", being posted!
Check out 5 short videos (10 minutes total) that show off what it (and WPF) can do:
http://www.microsoft.com/products/expression/en/demos.mspx?v=id_design
What do you think?
:-)