Notes iCloud "Notes can not currently be enabled"

Maybe enabling Mail would do it. Notes synchronises via IMAP mail accounts - do you have any?

Notes and Mail have nothing to do with each other in Mountain Lion. The fact that Notes uses IMAP for folder storage is immaterial here. Enabling Mail will do nothing here.

You need iCloud set up on all devices, and Notes sync needs to be enabled.

Yes, you are right, in that it should work without mail being set up, but the question remains, what can he do to make it work?

He's tried toggling on the other devices.

So in System Preferences->iCloud are you logged in on Mountain Lion? If not, you'll have issues for sure.

You don't need your @icloud.com email address. You need to use the same Apple ID that you use to log into iCloud on your iOS devices, with the same password. Then you can enable Notes in iCloud there and you'll see the iCloud area in the Notes application.

My thought was (even if it seems irrational to others): if you had another IMAP email account, you could try enabling Notes there, which might kick-start it. Maybe it has a problem writing the container (edit: which it most likely would with an IMAP as well).

Edit: or just try to install over it - that sometimes solves iCloud problems.

Maybe /Applications/Utilities/Console will tell you/us something? Launch it, make sure it's set to "All Messages", then go to your iCloud account in System Preferences and try to enable Notes again, watching the console messages appearing at the same time.

You could also make a note of the exact time and scroll down to the system.log (under "var/log", which may give further info on what's happening.

Have you tried logging out of iCloud and back in?

...everything

Now this I can't quite believe. 😀 (edit: also it would be of no use posting here, if you'd "tried everything", as nobody can suggest more than that)

So you've:

re-installed ML,

checked in a different user account that the problem exists there too,

and finally

wiped the drive and installed ML

I'm having the exact same issue. Did you finally solve it?