Gmail now has HTTPS enabled by default for the entire webmail site. Earlier, it was just the login page encrypted with HTTPS. This was protecting just your password from getting intercepted. This is so with most if not all of the webmail providers.
But it is a good move with Gmail to be the first webmail to have the entire site HTTPS encrypted. Looks like, Google had to upgrade their servers to provide better performance. I did not find any decrease in speed with the HTTPS site. A thumbs up for Gmail.
Read about the official annoucement here