I'm using Ubercart with D6 on a production site, albeit one without images, so Ubercart 6 can certainly be used if one understands the limitations.

http://www.clacom.com/

I am also working on another site that DOES use images and it too is working just fine. We are now tweaking the display to our liking, even have Thickbox working in the Catalog Grid.

http://www.inmatesgreetings.com/

The biggest stumbling block is the lack of Order Notifications. But, I got around that by using PHP in the Checkout Success page that sends me an E-Mail telling me that an order has been placed. It will work just fine until the Conditional Actions (CA) interface is finished.

Kenny