I have used IPortable to import and export items for months. It is really only useful for raw data dumps for testing. I also posted some sample code somewhere here that would import items and categories from an Excel spreadsheet.

The real problems are with live data using primary keys and nested categories. It works fine with the flat categories in v1.0 but it becomes a little more compilcated when syncronizing nested categories with items. I have experimented with a new product field called SKU which could be used to update or append on importing but the process is extremly slow.

In the mean time, if someone has some suggestions that will not break existing data - send psuedo code and I'll happily port it to c# or vb.