One of the most valuable lessons the IT industry learned in 2011 is that the cloud is not invincible. It's like any other IT system: It can crash. It can go down. It can be knocked offline by a lightning strike. While the cloud has proven itself as (oftentimes) more reliable than its on-premise counterparts, it's not 100 percent without flaw. That was proven several times over the course of the year with several high profile cloud outages. Here, we take a look at the 10 biggest cloud outages for 2011.