It could be an artifact of my postfix configuration. Looking over a few logfiles, here are the ciphers I've seen recently (all servers, not just gmail):
ADH-AES256-SHA (256/256 bits) AES128-SHA (128/128 bits) AES256-SHA (256/256 bits) DHE-RSA-AES256-SHA (256/256 bits) EDH-RSA-DES-CBC3-SHA (168/168 bits) RC4-SHA (128/128 bits)