I'm using the feeds module to synchronise a range of products across 2 commerce web sites. I have set up a view that exports the data from site A in XML format. On site B I have a feeds importer that grabs the XML and updates nodes accordingly. I have no trouble exporting the node weights via views, but weight does not appear as a target on the feeds side to map this to the imported nodes.
I haven't delved into the feeds developer documentation, but I believe a plugin may be required?