Joined Datafeedr for the comparison set tool, which is really cool. Don't know how feasible any of these things are, but they would make life a little easier when dealing with a large # of sets.
1) List all sets for a category in alpha order to make it easier to see which sets have already been created as you work through your product list
2) Indicate in product list if a product has already been added to a comparison set (maybe highlight with a certain color). I know you can click on the product and see if it's in a set already, but highlighting it in list view would save these extra clicks.
The following might be a little pie in the sky but I figured I would mention them.
3) When a merchant adds a product that already has a comparison set, it'd be great to either be notified that a new version has been added to a feed or have it automatically added to the set.
4) #3 makes me wonder if datafeedr has a mechanism that lets you know when new products are added to a feed in general. That would be nice for people to know what's the latest product to promote with a blog post or the like.