Whether you see this as a welcome adjustment to modern times on the part of an archaic figurehead or another case of social media ruining other social institutions is up to you. Personally, I'll walk that middle ground of "little bit of both".
Granted, this isn't Elizabeth signing up for an account and friending all of her pals from back in queen...school... It's the British monarchy establishing a fan page, which thousands joined by "liking" within hours.
Sadly, this means that you can't "poke" the Queen. But you were never allowed to poke the Queen anyway.