Until recently, HTTPS (secure web connections) were only used for pages that did not display ads, including the login page, etc. About a week ago, I started testing having HTTPS used for all pages. I'm happy to say that the test has gone well, and this change will be a permanent one.
What does this mean for you? Probably not much. Just know that the site now only uses secure connections, so when you're perusing CougarBoard on open wifi, people won't be able to see what pages you're viewing. And the NSA probably can't see now, either.
Although I wouldn't put too large a wager on the latter.