I found another reason for acquiring a .org over a .net and that is to weigh up the cost of buying the .net and .com and working out if your competition could afford them anyhow....... generally my order of preference would be .com then .net then .org and then finally ccTLD ... but there are plenty of exceptions on the type of site you are running (non profit, localized etc).
I own TESTING.ORG as I originally wanted testing.com or testing.net but the prices quoted for the .com were huge (many many zeros) and the .net was in use for another purpose. I found for what I want to develop the .org works fine but would likely not have been my choice over the .com and .net (possibly over the .net). The ccTLD (.co.uk for myself) would have worked well also locally but I couldn't reach the owner at the time.
Anyhow, that's my two cents.