A while back I had posted a question about the ability to access eBay Express items via the Search function in the eBay API.  I haven’t checked out the call myself yet, but you can see on the eBay roadmap they have already begun to integrate the Express results.  Below are notes from the eBay Developer Roadmap:

• GetSearchResultsExpress (should be available now)
  The new GetSearchResultsExpress API call will allow developers to access Express-specific items, products and domain histograms.
• REST Support for GetSearchResultsExpress (September ’06)
  Adds REST support for the GetSearchResultsExpress API call. Click here for details on the GetSearchResultsExpress API call.

I see this call as being be very useful specificly for mining marketplace item data from eBay.