I am guilty of the being one to abuse e-mail on several occasions. I think out loud in emails and go back and forth in planning and discussing. Sometimes its warranted, other times not. But my biggest pet-peeve is people hitting reply-all when it isn't really necessary..and especially when you don't even know the others in the address list. (I am talking about personal e-mail here). I just got wished "Happy Ugadi!!!" from a bunch of random folks I don't know just because my uncle sent all of us a single email with the wishes. Gah. And then, I did the unimaginable: hit "Reply All" to an email invitation to someone's party. It was an honest mistake- and I was so disgusted with myself I wasn't sure if I should do another reply-all to apologise for the mistake or just sit quiet. I decided to sit quiet, and now have lost all rights to bitch about the flurry of reply-alls that have ensued since.
I really think we need an additional button on gmail that says "You hit reply-all. Are you sure you want to inundate the mailboxes of ALL the people addressed in the original email, or will it suffice to just answer the sender of the e-mail?"