So it seems I've bigger iCloud issues than just not being able to get into the iWork apps on iCloud.com
My iMac and iPad won't talk to iCloud. Documents created on either of these won't update iCloud. The Open dialog in Number on my iMac (OS X 10.8.5) display the iCloud documents with "Waiting..." and never changes even after leaving it open over night. Updates from Day One which is set to sync over iCloud don't get uploaded/download on either machine. TweetBot syncs it's reading position over iCloud however. I've tried rebooting both the iMac and iPad, logging in and out of iCloud on both, and using the iPad on 3G and WiFi at work, and can't update with iCloud. My MacBook Air however syncs documents fine however, as does my iPhone 5 so it doesn't look like an account or network issue.
From what I can see by the last set of sync'd Day One entries and iWork files the iMac stopped syncing on Sunday (15th) night, around midnight UK time was the last iCloud update, and the iPad stopped syncing on Wednesday (18th) evening, possibly after updating to iOS 7.
One thing I am seeing in the system.log on my iMac are errors from librariand with the message "The operation couldn't be completed. (UBErrorDomain error 6 - The item is in cloud, but we couldn't reach the iCloud servers.)"