Three things which I would die for:
1) Keychain syncing (So annoying registering for a site on my iMac, then needing to remember a ridiculously long password on my MacBook Air, then perhaps a week later needing once again to remember it for my iPhone...)
2) "Save to iCloud" option on iWork, just hit Cmd+S and press the iCloud icon and bam, it saves. Also opening documents from iCloud would be great
3) Multiuser iCloud iDisk - would be great for sharing files from...