I don’t like the idea of putting all my stuff out there for someone else to store, or look through.
iCloud should have been named iNightmare from my perspective.
I don’t trust the concept at all.
But it just works so well. I got an email on the Mac from a new business contact. I hovered over the signature block, and Mail offered to make a contact out of it. I did so, and dude was in my contacts (it parsed everything perfectly). Both the computer and my iPhone are hooked to iCloud, so later when I went to call him, the full contact was already there. I could also have the most seamless bookmark syncing out there, but I still use Firefox.
The cloud has also saved me money. I use iTunes match to get songs on my iPhone synced with my computer. So now my 16 GB iPhone has access to my 40+ GB of music (the service even upgraded most of my music to 256 kb). Why buy a 64 GB phone? I burn a new CD or download a new song, and there it is, available on the iPhone.
OTOH, none of this is worth anything to anybody, or more personal than the basic contact list. The most valuable thing is one credit card number, for an account with very limited credit. Now when you start storing very sensitive personal data, or mission-critical enterprise data, then I definitely have problems with the clouds as they are today.