I recently turned up a site (in a beta version) for my client using Ubercart. The url is: http://www.pencils.com/
Aside from core Ubercart (with uc_usps, thanks Lyle for adding my patch to core), this site is also using uc_aac with some small modifications, uc_product_min, and uc_discounts (with a bunch of fixes).
I was attempting to get userpoints_ubercart integrated before the beta, but it seems that it needs a bit of work. I'll be working on this for pencils.com, and hopefully be able to contribute my development back, if it fits the needs of the module. There will also probably be some integration between uc_discounts and userpoints_ubercart.
I was originally building this using ecommerce 3.4, but the "killer feature" that brought me to Ubercart was the attribute system.