Some stats from Stack Overflow

Questions with no answers:  
75,422 / 1m+
 
Questions with no answers and score > 0:  
12,705 / 1m+

Questions with no answers and score < 0:  
2,016 / 1m+

Questions with no answers created more than 30 days ago:  
64,717 / 1m+

Questions with no answers created more than 120 days ago:  
39,915 / 1m+

Questions with no answers and score < 0 created more than 30 days ago:  
[1,631 / 1m+][1]

oldest zero answer question in the system:  
http://stackoverflow.com/questions/87110

Based on this data, **I am only comfortable auto-deleting the negatively voted, zero answer questions more than 30 days old**. These are basically complete crap, and they're a tiny minority of questions anyway.


  [1]: http://odata.stackexchange.com/stackoverflow/q/13467/non-deleted-questions-with-no-answers-and-a-negative-score