Minecraft's login server (session.minecraft.net) is having issues, so if you can't log into the server, it is probably that. There is no need to make a new post about this, there is nothing anyone can do about it, we just have to wait for Mojang to get around to fixing it.
Just look on the minecraft forums, there's always a lot of posts about this everytime it happens.
http://www.minecraftforum.net/topic/1148892- (this one has some good info if you're curious why it happens)
And all the top posts in this forum:
http://www.minecraftforum.net/forum/152-server-support/
update: They are finally aware of it.



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