My own feedback so far: Clicking download, should allow me to download the document. It should not require me to create a dummy account, jump through 'invite friends' 'look at these other documents' hoops.
Also I really like the way Google has a scrollable list of thumbnailed pages. Makes navigation very easy. Also search, and ability to change size of pages with a simple click to allow different reading modes. Plus with Google, when you click [download], it downloads. It doesn't try and get you to sign up.
Scribd looks like a big improvement on flash definitely though. The fact it's using fonts rather than fonts rendered on an image is lost on me though. Copy+Paste of text works fine in both viewers, and that's all that really matters to me.