If you're like me, you rely pretty heavily on Apple's iCloud services for email, calendaring, tasks, photo sharing, iTunes, etc. I consider these services the glue that holds our Apple devices together and keeps them all in sync. Without it, these devices are just a little less smart.
It's clear that Apple feels the same. So much so that they have invested a lot of money in several new datacenters, located around the country. Occasionally, even with all the money that Apple continually invests into these datacenters, technical issues prevail to the point that it can directly affect our ability to access some of their services.
Fortunately, Apple has been kind enough to give us a way to check out the status of each of their services. If we're having email issues, for example, we can use this as a source of validation of the problem.
Not only does this site give you real-time information about each service individually, but it will give you historical information once a system is back online (so that you know what the issue was and how long it lasted).
When you get a chance, you should check it out. It's very interesting.