Actually, the "duplicate entry" for table term_node is a warning we get too. But only a few warnings for around 2000 products imported. After the import I checked out the number of records in the different tables and the count for uc_products, term_node, content_type_custom, node, and a few more were correct so I just disregarded the "warnings".
If you find out why these warnings happens please post back though

This is how we used the csv import:
-First I create a custom product class
-Add all the necessary fields to the new node type (this includes the image field)
-Upload product images to a place on the server accessible to apache (the webserver)
-Go to the import csv url and select the csv file for upload, select the class for the products I'm about to import, and limited the module to -only- generate the xml-file for import. We don't have a column in the csv file which specifies the product class (might have something to do with the message you are seeing)
-Save the generated XML file to disk
-Use the ordinary import module to import the XML file

The only messages I get from the modules are number of csv lines processed, number of products created (written to the xml file), and some of the same warnings you got.