Shopify, which serves up do-it-yourself sales pages to sell your all sorts of items (including your junk, as Rafe experimented with in his hands-on) launched an interesting new feature this week called Marketplace. It links up people's Shopify stores to a central index that can be searched, sorted, and browsed by anyone and everyone. Owners of each Shopify store must opt-in to the program to be included, in the hopes of selling an item, or being discovered through the centralized directory. Shopify is also releasing an API in the coming weeks that will let developers tap into the new data stream with their own apps. There's already a widget for Apple's Dashboard that serves as an example of what you can do.
The search experience itself is lightweight and easy on the eyes. Results can be sorted by tags, product type, and the vendor--which is helpful because items tend to get lumped together. Each item has its own photo and short description, along with links to the parent store.
Of course you're not going to find nearly the scope of items that you'd find compared to services like Google product search, or established classified listings like Craigslist or eBay, but keep in mind that Shopify is indexing a list of about 20,000 smaller shops, and many of the offerings are niche.