Death to the email "Reply" button!! Long live "Reply All"!!
One of the more frustrating behaviors I find in the online world is when people click "Reply" to an email instead of "Reply to All" (or whatever is similar on their email app). Why clicking "Reply" is a bad habit is that usually other email addresses on the email that need to be kept in the loop are dropped.
When I joined Microsoft I was in such a bad habit of clicking the Reply button that I removed it entirely from the Outlook toolbar (right-click on the toolbar, choose Customize, then drag the button off). This made my life so much easier, just having the "Reply All" button visible. Alt-L became my friend. Now this is a standard practice at my current company. (see this little video on how to remove the Office 2007 "Reply" button)
Of course there are cases when you need only reply to the one individual that sent a mail to a long list of recipients, but I find these to be the exception rather than the rule, and it is still very easy to remove email addresses from a reply.
Google Gmail gets this. The very first Labs option (under Settings > Labs) is an option to make the "Reply to all" button the default.
The Call to Action
So my call to anyone that does email, please, help destroy the "Reply" button and remove it from your Outlook toolbar or other email client. Help make the world a more peaceful place by facilitating better communications and use the "Reply to All" button instead.