From a recent article in The Register (UK):
We might continue to buy our Apple gear, but every time we buy a Samsung or Amazon or Google device, we’re going to be reminded why we don’t keep our content in iCloud, but instead keep it with Amazon or Google or Microsoft SkyDrive. These other services “just work.” Apple’s cloud? Not so much.
The author, Matt Asay, writes that his household owns: five Macs, two iPads, and four iPhones all running the latest OSes).
I’ve written before that Apple’s closed system is eventually going to get it into trouble, despite its insanely great hardware and OSes. A couple of days ago, my wife’s .me e-mail stopped working. We had moved her over to iCloud several weeks ago and it had been working fine. It stopped working on all platforms — iPhone, iPad, our two Macs, and through icloud.com, and whether accessed through our home network or over ATT mobile. She can log on to her account on icloud.com, but when she tries to check Mail, she gets a “Not available” message. When she tries to check from Mail on her computer or iOS devices, she gets an”incorrect username or password” message.
Because her system is over 4 years old, Apple support won’t talk to her. All we can tell from the discussion boards is that other people have the same problem. Other than the “send report to Apple” box from icloud.com, I can’t find any way to report the problem.
As I type this (on my MacBook), she’s busy converting all her accounts over to her new gmail address (I had already set her up on Dropbox). When Apple’s latest earnings were announced, she cheered.
Slightly East of New 
People need to understand, as much as they don’t want to, in the modern tech world, not updating your OS is not an option.
This is true.
Unfortunately, all our devices are running the latest versions with current updates with the exception of my wife’s computer, which is still running Snow Leopard (not enough memory for Lion).
Update: My wife’s iPhone is still in warranty, so I used it to call Apple Care (even though what she has is not an iPhone issue). The tech was very helpful, although he said he needed to run a series of diagnostics on her phone before referring me to iCloud support. Fair enough, even though I had told him that she has the same problems on her iPad and MacBook.
To make a long story short, iCloud has verified that there was a problem moving her e-mail account to a new server, and as soon as they fix it, they’ll let her know. It must be an interesting problem because they’ve been working on it since Friday (I know they’re working on it because they’ve called back to ask me to check her system — so far, no luck).
I have no complaints. They’re aware of the issue, and I have every confidence it will get fixed.