I would ask to you and ALL the ones who are having this problem to click SENDO ERROR TO APPLE, on icloud homepage. May be we have an answer, Thanks
I'm having the same problem and spend nearly 2 hours on the phone with apple tech support to no avail. I was told it was isolated to my ID (obviously not). Not sure about your situation but I am able to see my calendar and contacts just not email. The informed me it might be a "server glitch" that might resolve itself tomorrow. If it is not resolved tomorrow they will have to send it to their engineers to troubleshoot, unfortunately for me the engineers don't work on the weekend. Overall they seemed really unconcerned about which I find unacceptable. I'd suggest contacting tech support so they see that more people are having the issue.
In respone to gianlorenzo, I did send the report to apple as well, support seemed to be unconcerned with that as well.