Previously, you have the option to use either http or https, as of today they will be implementing the use of https as the default. However, you can still turn it off if you want to. The effects of using https will mean slower processing of emails but I think security should be a priority.
The reason why Google implemented this was when they detected a "highly sophisticated and targeted attack" that resulted in intellectual property theft and the attempted hacking & accessing of Chinese/US/EU human rights activists Gmail addresses.
I'm thinking that since not everyone uses Gmail, the other web email providers like Yahoo! and MSN will most likely have had the same experience. Hopefully the other web email providers will also default to https (if they haven't done so) after this event for the sake of their users.
