rstevenson:
Since you're already using Easy Populate, and presumably create and maintain your base data in Excel or a similar program, you could automate the process somewhat by using Visual Basic within Excel. But of course, this would mean you'd always be deleting and creating categories as needed rather than just turning them off and on, and I'm not sure EP can delete categories during uploads -- create yes, but maybe not delete.
Rob
Well, I'm not really maintaining the whole thing with excel/easy populate - I just use it when adding new products and changing stock status. There are a lot of things EP doesn't do, or doesn't do well (most annoyingly - sort orders, and item attributes, but also category management as you noted above), and sometimes I can complete the picture with some SQL queries, but for this I'd need something more dynamic.
However, your post got me thinking.... maybe there's a way to add a little routine to Easy Populate's php scripts, which would run after an EP file has been uploaded, loop through all the categories, count the active items, and change the category status accordingly. Could be a nasty bit of code-crunching (for me) but might work....