On behalf of a Munich based Internet Agency we migrated the whole content for a online shop from the old XTcommerce system to the Magento community edition.
We were responsible only for the data migration; design, business logic and integration was done by the local team.
We were forced to do the migration in 3 steps in order to get optimal results. First we only migrated the products. Then we assigned the products to their corresponding categories. In the last step we were able to merge the 2 languages, German and English into one version.