The limit is still a problem for me. Once more worker machines come online I'll be having the listen length issue again.
All of my worker processes (not threads due to Python GIL) talk to MongoDB. I end up with over 1,000 connections to MongoDB and all of those happen at startup virtually instantaneously (lots of forks).
I'm rather sceptical that one size will fit everyone hence a need for it to be configurable. There is a reason why virtually every UNIX daemon that will serve non-trivial loads has it as a configurable, and rarely use the OS default of 5.
As an example something else I use is gearman which takes --backlog and a default of 32. MySql takes --back_log and I don't know what the default is. I don't run postgres so I can't tell what it does, but I did find a CVS commit from last year making the listen backlog configurable.
So it is evident that other databases and similar system components had the need to make the value configurable. What makes using MongoDB so special that its default is the perfect value for everyone?