If you recently upgraded to Emacs 23 from Carbon Emacs on your Mac you might have found all the control keys are bound wrong. Anyway it’s easy to fix, add these lines to your .emacs and restart Emacs.

; Setup the Mac keys
(setq mac-option-key-is-meta nil)
(setq mac-command-key-is-meta t)
(setq mac-option-modifier nil)
(setq mac-command-modifier 'meta)
(global-set-key (kbd "<kp-delete>") 'delete-char)