This feature is an important one for me. Documentation is very limited and it seems a lot of functionality is missing. I'm not sure how much since I haven't gotten very deep into testing yet, but I've already had to go into the database to edit things I should be able to view/edit from the admin panel.
 
So anyway, I would like to hear from anyone who is actually using this feature. What is working for you and what limitations have you encountered? I'd like to get an idea of what to expect or look out for as I'm testing.

I'm currently utilizing this in beta mode right now. I'm attempting to go live with it, where my merchants can add their own products.
 
I'm thinking about a customization to allow import of products via csv file.
 
Also, limitation is that I cannot know or edit what products belong to what merchant.

That's a good idea - I was thinking an import feature would be nice.
 
With my current cart, my merchants send me the csv file and I upload and manage everything. I have reporting issues too as I have to download the database file and sort it into spreadsheets to come up with how much to pay and let them know what was purchased. I'm hoping the reporting is easier with ViArt... I haven't even made it to testing that yet. I'm scared.