The popup happens when you send mail to a character that is not yours. I get no popup sending to an alt, but the mail I sent to a guildie yesterday gets a popup. I don't regularly send mail to characters not my own, so it's not that big of a deal, but it is slightly frustrating that the popup should know who my guildies are.
I assume trading has this new confirm box as well. The confirm button is even delayed about a second or so to prevent accidental clicks. It may also prevent code from circumventing it.
OT: Petrah, after reading your signature, have you seen
!sh?