After mucking around with it a bit, I discovered it's similar to Amazon or Zazzle widgets - you create a store then add it to your website. The difference is you can mix and match products from several different affiliate networks.
Not relevant to HP but I might have to look into it a bit more for my websites.
You might want to also consider Golden Can - it's free for many merchants and for others they take each fourth click - similar to HubPages taking a percentage of impressions.
Oh to answer your question. Yes, I have used popshops extensively. I got very concerned at one point when I realized how much of my livelihood was dependent on a new company. It's a very effective way to build lots of product pages quickly and to customize it. So now I also use golden can. And when I work with Shareasale merchants I use their Make a Page Feature.
There's also a program called webmerge that I use. And sometimes I just make the links myself.
Marissa did you see that I edited my comments? And I think that these programs are really useful if you build your own content around them. Similar to the way we write hubs. If you just throw up the product displays, it doesn't work so wellat ranking in search engines or converting traffic.
I also love the ease of which you can add products to a wordpress press blog.