First it is important to see : icloud it is not a virtual harddisk like "idisk". It is a much more theoretical "storage". Servers spreaded all over the World. "Distributed storage" so to say.
Like you said, it is space from Apple that stores your data.
iCloud enabled Apps are so to say "Frontends" to let you see and use the data like iCal,Adressbook,Mail.
On www.icloud.com you have direct access to your uploaded office files which iwork for iOS has stored in the cloud, these can be downloaded to Mac/PC. But other "Storage" there is none.
Your Apps,ibooks are backed up by Apple in their iTunes/AppStore Servers. These also do not count to your 5GB limit. Again this is "Apple space".
Your Camera Photo Roll and stored documents in iOS is backed up to the cloud, but you have no direct access.These backup is used if you need to reinstall your device, it restores "over the air" from that backup.
To peek inside the occupied space ( and delete stuff ) you can use the icloud controlpanel in Windows or this setting in Lion on a Mac :
Thanks for this! How comes, when I try to update both my ipad and iphone i do not see my info/data on the cloud? Why is it not updating? I mean there is just one account right...One cloud. Then both my iphone and ipad sync to that same exact info. Correct? So there is only one log in to one cloud for all devices correct?