I have built three ecommerce websites using Interchange. Two of these sites are in the Interchange Hall of Fame. Interchange is good for building a powerful, full featured website without a huge amount of work. It is fast, has an amazing back end, and it is free.
The reason i give Interchange a 2 star rating is because it is VERY VERY DIFFICULT to make changes to your store. Interchange uses it's own very bizzare programing language not based on php, perl or anything else. Changes that should take about 45 minutes to make using php or perl have taken me 8 hours with Interchange. This has happened to me on numerous occassions.
So if you are planning to make changes and additions to your store, do not use interchange. however if you are happy with a canned site with powerful features, interchange is great once you get past the tricky install.