I just finished coding up a new addition to discount codes -- the ability to specify valid categories for your discount codes. This enables you to customize which discount codes work for which items. Remember, you can place items in multiple categories, so you could create a separate “Sale” category, place items in that category using the “Batch edit” function, and then specify that your discount code only work on items in that “Sale” category.
A few things to note:
Hope this comes in handy over the holiday season!