Starting today migration from Yahoo Store is supported by Cart2Cart. You can transfer all the data from Yahoo Store to the shopping cart of your choice. Currently you will be able to move the following entities: currencies, manufacturers, product categories, products, product attributes and product images. Migration of other entities will be available soon. Please note that you need to have Product Catalog enabled in your Yahoo Store to perform the migration.
Cart2Cart is a first web service that allows to migrate from Yahoo Store automatically. You'll simply need to specify the URL of your store.