Matty,
I have direct experience with it, and have seen it's progresssion from it original purchase from Brice Snow at Snowcovered. Basically, this is the Snowcovered Store a few rev's removed under the studious care of Richard (dnn-modules).
I think the world of Richard and his product line. His support has been fantastic. However, I have tried on 4 occasions now to implement the DNN-Modules store. Each time the client felt it was too complex, and asked if there were other options.
Each time I showed them the store mentioned earlier (only second to showing Richards Store, as I wanted it all in DNN). In each time they chose not to implement the DNN-modules store. 3 went on to use the aspdotnetstorefront, and 1 went with a Linux/Ruby solution.
I have a very large interest in using a DNN / DNN eCommerce solution. But one hasn't yet presented itself. So I wait on the CORE Store. I have offered a suggestions 'here and there' as to how certain provider-model pieces might make it more extensible, however, there are larger issue looming here than eCommerce (ie. the membership model change).
So with a paying client, and high expectations, I went non-DNN... for now....
The store's I mentioned are:
http://www.globaldecor.com/
http://www.starletteohara.com/
http://www.bsi123.com/
The Linux/Ruby Solution I didn't end up doing so I am not sure on it's final URL or success.
Hope that helps,