Sebastian is correct - Catalook isn't the prettiest picture at the moment but it does allow for tremendous flexibility in designing an ecommerce site.
You have the images already so that's a great help. And if you can work with an xls sheet you can manage much of your site this way quite efficiently and in small steps.
EG - http://www.inkandtoneronline.com.au (NOT FINISHED but it's live) each product range has it's own xls sheet - and as it's been corrected, has been uploaded invidually. I have been working with this client for quite a while now but he's basically done all the content and sourced the images himself, and that site took us about 2 hours to get running, after all the content / xls sheets and images were provided. But don't think it's that easy OK - because the primary site - http://www.stationersonline.com.au took us a few months to get right - mainly because there were problems with the format of the XLS sheet -eg.. UTF7 & UTF8 stopping it from being imported.
http://www.style.net.au - that's about to have a face lift again- but that's running from an MDB file which has been imported- this took a while to get right - but the client has modified his access driven system and it now works really well.
http://www.chalkartstudio.com - that's managed by the sign writer - and we still have some issues with the xls formatting, but the whole site overall has been self managed, once we got the structure in place, and there are plenty of other sites around - this is one I came across today - http://www.beachbeautiful.com/
So while we don't have thousands of sites using ecommerce yet, I think this gives some little examples on how it can be transformed.
There is also the manual online at http://www.catalooksupport.com which gives a bit more information on how the store can be managed.
I have some other very nice sites coming up with Catalook but like anything they take time to develop and they aren't available just yet.
What is quite unique about DotNetNuke and the ecommerce that can be attached, is that not other solutions offer such a "plug and play" method of growing your website. Either it's ecommerce or it's not, so it's been well accepted, and another thing is the skinning aspect of it. I think DNN provides the most flexibility to create a unique look and feel and to integrate it with ecommerce, well, that's just another great reason to use it.
Hope this helps you with your decision making process.
Nina Meiers