I know I'm a relative noob to uBercart but from my perspective I'd like to see

(1) more flexible shipping rates per product - either several fixed rates or perhaps country based?
(2) auto-adding VAT for UK customers (obviously, being English means I'm biased)
(3) a BUYITNOW option to pass the first item name as well as order number to paypal - purely selfish reasons
(4) discount-codes or promo-coupons

ehm.... thats it for now. Cheers.