They decided to move the servers to a more modern data centre and unforeseen issues with the Database server during testing has caused the downtime to stretch almost 24 hours longer than expected. Of course the haters pour out of the woodwork to decry CCP's ineptitude which is hardly fair since we don't know exactly what went wrong and what could have been done to prevent it. Then you have the people complaining about the lack of information but really I prefer they spend their effort fixing the issue and then tomorrow telling me what went wrong.
This is the first time in a long time CCP has had a downtime so much longer than expected and I bet the skill training horse with a 12 hour buffer for my alt. Whoops! Oh well. At the end of the day, we need to remember that us paying customers didn't get about 50 cents worth of playtime we paid for.
This is the high tech world, accidents/bugs happen and when they do fixing them can be an effort and a half. Let's wait and see what the incidence was and if common sense could have prevented it before stringing them from the highest tree.