Among most often custom coding tasks are usually those related to some import/export between Magento and other system. Usually existing store owners when switching from their current shop system to Magento want to transfer all of their products, orders, and most importantly customers.
Most of the time, standard Magento product/customer import/export is not sufficient for the task at hand. Limitations like file size upload and structure of original data require you to do a custom scripts that will handle the job of data transfer. Think of shops with several tens of thousands of orders, customers, products.
Luckily Magento comes with several nice classes that handle files and directory manipulation that might help you greatly. Surely all of this can be done with plain functional PHP, but hey why not impress your boss right?!