This is not my hint, but I'm reporting it here after seeing it posted elsewhere. Phillip Moore found a solution for occasional tcsh: no more processes and similar errors. Check his original post for details and the discussion.
One modifies /etc/launchd.conf by adding this line:
limit maxproc 512 2048
A restart is then required to activate the new settings. Or find some other way to restart launchd, which I didn't feel comfortable doing. I'd run into this problem sometimes after opening multiple Terminals and running a bunch of shell scripts.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060315121122636