So I was reading Laurie's post yesterday on her blog about pet peeves. We agree on a lot of things, not all cat related either. It seems we both have issues with the "reply all" option on e-mails.
When you receive an e-mail as a part of a larger group (for instance, when a message is sent to the entire staff) it is not necessary to reply to the entire group. It's great to receive an e-mail to notify you that there are fresh cookies in the office kitchen, it's not so great to receive 5 replies to that e-mail commenting on the quality of the cookies.
In my opinion at least, the "reply all" feature should be removed entirely from all e-mail programs. At least make it hard for the user to find. We all waste too much time each day as it is wading through e-mail, we don't need to waste any more.