I asked about Ubercart and POS integration at tonight's Meetup at Duke Corporate Education. One short Google later and here's what I found:
From the front page of the site:
uberPOS is an open source point-of-sales system built on top of the Drupal Content Management System (CMS).
With uberPOS you can:
Easily and quickly add and remove products with a scan gun
Set up membership discounts
Accept cash, checks, credit cards
Print customizable receipts
Give refunds
Customize the interface for your shop
...and more
As I'm a complete n00b, and a designer/themer I'm not really sure how to evaluate this solution, but it looks pretty cool on paper. Especially if the ability to run a web shop and a brick-and-mortar at the same time works as promised. It could be interesting to do this for a client some time. Hope this helps!