After an unceremonious crash of Terminal.app, I restarted and found myself unable to open a second terminal window. The first window worked just fine, but the second would immediately close with no notice or crash log.
After trashing preferences and sacrificing a chicken to the bash(1) gods, a ps -ef revealed that my processes from the previous terminal session were still running, and thereby monopolizing my ttyp2, where the second terminal window should attach. Once I killed all those processes with kill(1), I was able to open the second window.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030211071115558