Just thought I would share this. I am not a long-term user of either Ubercart or Drupal Commerce, however I have recently installed both with a view to developing a production site, using Drupal 7.
In fairness, my new regard for Ubercart (not that I disliked it before) is partly due to Drupal Commerce being a bit of a monster at the moment. It seems to want to create endless database entries, was uninstallable for me (I ended up re-installing Drupal 7 after not being able to unistall Commerce), and is not as intuitive as Ubercart.
I am not sure what Commerce is supposed to be, but from the admin perspective it feels like an old / unfiinished and less user-friendly version of Ubercart. I'm sure there are reasons for how it is, but I couldn't see any advantages (although I didn't delve into the code).
It actually seems a shame that developers left to fork Ubercart, and then create something less likely to appeal to the masses, while pulling developers out of Ubercart. Never have been a fan of forking, and this experience doesn't change my view.
So, I guess all I really want to say is, whatever Ubercart are doing, keep doing it. With Drupal's growing popularity, this could be THE cart taken into account any system, not just the current leader for Drupal.