The only complication is the fact that they use client side SSL certificates for authentication. I don't know of any other site which does this. Although I like that they're dog fooding, it probably would have been better if they'd stuck with a traditional username/password/cookie scheme for logging in, from a business/usability perspective.
It confused me a lot because I used to have an old username/password account with them and when I tried to sign in and got a very generic SSL error from Firefox.
That said, once I registered with a new account, the client certificate worked great.
