Emacs in Mac OS X 10.1.3 (and other versions) has an annoying habit of having broken shells when you do M-x shell. You get an error like "Inappropriate ioctl for device, no job control in this shell", which makes interrupting or backgrounding programs in shell mode impossible. Domo-kun gave me a one-line patch to the emacs source:
. Add that to darwin.h and build emacs. You can get the emacs source from the Darwin projects page. If you'd like a binary, drop us some mail.