I thought this was sort of an interesting Microsoft KB article.
OL2000: Preventing Reply All to Large Aliases
In a nutshell the offer 3 methods. The first is simply to use the Bcc: line (duh). The second is the most interesting and clever to me, create a custom Mail Message Form which has no Reply to All button. Recipients could still use other Reply to All methods but it would foil the unconscious hitting of that button because IT WOULDN'T BE THERE! The third is to use a system policy which disables all Reply to All methods in Outlook. If you're the kind of sysadmin who roots for the "bulls" in prison movies, that's the option for you.