Does anyone have recommendations on how to report on historical out of stock %? Something like how many days in the last 30 has an item had inventory at a given location?

I have never seen an out of stock report for NetSuite. NetSuite just tells you to run inventory valuation and see what is at 0. You would have to do this everyday to get a true out of stock report. My company throws the Purchase/Inventory detail into our database every night. Then created an out of stock using that data.

I think the best way to do this is to create a saved search, then have a scheduled script use that saved search and update the item record at the end or beginning of the day.