I'm really impressed that I was able to bulk update Keywords on Sell Media Items. Note that this is a custom taxonomy on a custom post type. Impressive! Even the Sell Media plugin authors said "Nope, you cannot bulk-upload keywords"
I got the WSOD a few times, which might scare some WP noobs (like the bloke who gave it one star), but this was expected as I was updating 4000 items. Not enough to warrant anything less than 5 stars.