I've been using HTTPS to access Facebook ever since the social network offered it, but with over one billion users - having it by default is a much better way of keeping your users' data more secure.
Facebook has used HTTPS (Hypertext Transfer Protocol Secure) to protect users when they submit their username and password to login - which prevents someone from diving in and accessing your username or password when typing it. But, in January of 2011, the social network starting offering users to opt in for all of their Facebook browsing to fall under the more secure HTTPS umbrella, at the time warning "Encrypted pages take longer to load, so you may notice that Facebook is slower using HTTPS."
Facebook also said that "We hope to offer HTTPS as a default whenever you are using Facebook sometime in the future." We're finally here, and they're about to press the GO button on this more secure way of browsing. A few days ago, a Facebook Developer Blog post hinted that "this week, we're starting to roll out HTTPS for all North America users and will be soon rolling out to the rest of the world".
When this rolls in, users currently not using HTTPS will experience a slight slow down changing to HTTPS - but its not that bad. People will obviously complain of the slow down, but there would be a hundred times more complaint if their accounts were hacked. You can't have it both ways (at the moment), but we would highly recommend keeping the opted-in HTTPS option.