I'm really impressed with the rendering-animation and the envelope-sending-animation. It gives this app an air of a professional app. Kinda reminds me of the windows 95 file copy dialog. I realize that Silverlight allows for one man to create a big app as this, but they should have consulted a designer.
(this, BTW, means i watched it to the end, kudos for that)
Too bad this wasn't an open source project. I'm sure they could have found a designer willing to do it for free out of the goodness of his heart.