Doesn't everyone know that all the really top secret stuff always uses a GMail address without any encryption or other security measures? ...Ya sure, you betcha!
-Commerce
PS @copper: Actually, some of these messages do tend to help identify the so called "bad neighborhood" networks and "0wn3d" systems. Wish that GMail would actually always include the IP of the original client sender in their headers... Not strictly speaking part of the spec (the spec predates form mail, but arguably from a "spirit of the spec" standpoint it would make filtering that much easier).