The only usability issue I've really come into contact with is the degradation of Javascript in the shopping cart (fetching quotes and displaying the payment method, especially).. but if people don't have JS enabled that's their own fault 
Other than that, I have my own uc_file_retro contrib to add for Beta, since Shawn took that function out of the uc_file module in anticipation - so I'll try to finish that out this weekend for you guys.
Congrats on going Beta! (Can I have an Early Adopter badge?)