Why snail-mail is best for whistleblowers

Wikileaks founder Julian Assange gave some useful advice to journalists about protecting whistleblowers. Basically don’t use Google for anything, especially not e-mail, nor to store compromising documents in the cloud.
Google is very unlikely to go to court to protect your privacy, he said. Better to use snail-mail, and to encrypt the CD or memory stick that contains the good stuff. Of course, you still need to get the decrypt key to your recipient. But that should be less of a problem, unless you include it in the mailed package.
Downtime reckons you could also try that cute steganography stuff that the newly-swopped Russian spies were using. Yes, they got caught, but the spooks are probably watching you less closely than flame-haired lookers with come-hither eyes.