ICloud sync problems with 10.9.3

Question

Over the last 2 months I've noticed that from time to time my Notes & Calender stop syncing to iCloud from my MacBookPro.  For example, the Notes window has "Updating ..." tacked onto the window title bar.  When this happens, it's often the case that the iCloud pane in System Preferences won't open.
Other discussions suggest checking accounts etc but this clearly isn't the problem since iCloud syncing starts working again after a restart.
Any ideas?  Should I try a system re-install?

Answer 1

I think I have solved the problem myself (but thanks again Csound1 for your suggestion as it made me try other remedies.)
There are two almost identical MacBook Pros in our home (mine and my wife's) and I keep them synced at intervals.  I think the problem may have been to do with the fact that my account on each computer uses iCloud for Notes, Calendar and Mail accounts, and in some way the two Macs had become too identical so that iCloud was not distinguishing between them, leading to what I think system programmers call a 'deadly embrace' (each Mac waiting for the other to finish some task, like two ultra polite people trying to let each other go through a door first).  Since carrying out the steps below on 20th June, iCloud sync has been working perfectly, Mail has stopped crashing, and the iCloud pane in System preferences always opens when I select it.  In fact I have not had to use Force Quit at all since that date, and I have not restarted my computer (just let it sleep when not in use).
What I did was:
Step 1: made backups or archives of all mailboxes, notes, calendars and contacts from my Mac (anything that had anything to do with iCloud).
Step 2: on my Mac from System Preferences, selected the iCloud control pane, turned off iCloud syncing for all options individually, accepting any advisories that data copies would be deleted from my Mac.
Step 3: still in the iCloud pane of System Preferences, logged my Mac out of iCloud.
Step 4: repeated steps 2 and 3 for my duplicate account on my wife's Mac.
Step 5: restarted both Macs.
Step 6: on each Mac, logged back into iCloud and re-enabled iCloud syncing where wanted. [In the case of contacts, I deleted all contacts on the Mac completely first as otherwise you end up with duplicated entries as the data from iCloud is merged with the data on the Mac itself.] All the iCloud data was then correctly downloaded onto each Mac, and I did not need the backups I had made (but of course one should always make backups before carrying out any major re-organisation).
I have also checked my cross-Mac syncing procedures, and now I only sync folders that I know hold user content.  This means anything that's not in ~/Library (the user's library), but it can also include some folders in the library such as mailboxes.  Of course there's no point re-syncing anything set up to sync via iCloud (such as notes, calendars and contacts), but even if you select Mail in iCloud preferences actual mail messages aren't included, hence the need to sync ~/Library/Mail if you keep mail on your computer (as I do) rather than relying in an IMAP mail server.
That was it, and as I said, it seems to be holding good.
Hope these notes will be helpful to someone else.