It's worth as much as someone is prepared to pay for it.
What I mean by this: I sold a 3-letter .net for $x,xxx (you have to read DNJournal) :-D and the letters were not bad, but they were not great either. Sold a "bad" letter LLL .net for a similar amount. And I'm in the process of selling another one for 5 figures. 3-letter .net domain prices are on the rise, folks. They're almost where 3-letter .com's were at 3 years ago.
Practically, OOO.net would have to have a particular use. Even though it's easy to remember etc. I would say that its *inherent* value is $1k - $2k
The secret lies in finding a buyer that would ignore the reseller's approach and pay the "big bucks" for it based on his personal reasons and interest.