One of Google's least known services, Google Catalogs, was taken offline as reported by Gary Price of Search Engine Watch yesterday. It has been a long time since Google has updated the searchable content on this service which would explain its lack of popularity.
For more information on the first version of Google Catalogs, you can check out their old help pages -- still online since the site was removed.
The technology Google used for this service was very similar to what they are using for their book scanning project. They are likely going to try and take another run at it by restructuring their database (or would they use Google Base?) and upgrading their scanning equipment to make this service useful once again.
I am not sure how useful this service is though -- considering merchants could upload all of their products to Froogle and achieve the same (if not better) results. There is a "cool" factor when it comes to searching catalogs, but I'm not convinced of its utility unless the next incarnation of this service provides some extra features that I am not aware of.