Maybe it’s not as secure as you think. According it this article and the following post on Slashdot, Hushmail has been caught red-handed in backstabbing their own marketing.
"The only way to decrypt or unscramble Hush messages is by using your passphrase when you open up your Hushmail account. Carnivore cannot decrypt your mail, and is therefore, powerless against messages sent between Hush users."
Now it seems that they have handed over the private keys of users to the government, and thus voided their own technology. I would guess that they soon will have a few trust issues with their customers. I am not going to discuss the old saying, "if you are not doing anything wrong, why do you worry about the government reading your email".
At the same time some people within the U.S. government wants to redefine "privacy" so that it doesn’t include anonymity, and that NSA seems to have included a backdoor to a random number generator for use in encryption programs.