The authentication servers at Mojang are down for the moment, so you can’t login and play on any Minecraft server. Hope they will solve their problems soon.
A quote from Daniel Frisk’s Twitter, chief arhitect at Mojang:
There seems to be some kind of attack on our servers. DDoS is for losers who can’t hack properly.
Oh the irony… Should I feel humbled that we seem high profile enough that DDOS kiddies attacked us mere minutes before Mojang, or sad that said kiddies have no life?