Mac OS X limits number of processes to 266 and open files to 256. Sometimes this is problem; 256 open files and 266 processes aren't that much.
How it's possible to change default ulimit values in Mac OS X 10.6.7?
(Hopefully there's no difference between 10.6.7 and other Snow Leopard releases.)
Related question in serverfault. Unfortunately, answer is for Mac OS X 10.5, and it's not working in 10.6.