Gmail did have options before for HTTPS, but now they’re here by default.
And according to the website press, updated today [01/14/2010], even if you turn off the HTTPS session the login page will always be encrypted.
HTTPS encryption keeps your mail secure as it travels between your web browser and Gmail servers, so someone sharing your favorite coffee shop’s public wifi can’t maliciously read it. Banks and credit card companies use this same protocol to keep your online accounts safe. To protect your Gmail account, we’ve turned on the option to "always use HTTPS" for everyone. This added layer of security can make Gmail slower, so if you don’t use unencrypted wireless connections, you can choose to disable this option in your account Settings. Even if you change this setting, Gmail will always encrypt the login page to protect your password.
This is a good thing.