A true cloud service decouples your usage from your data. Email has almost always been "cloud" (IMAP, anyway).
Dropbox and Flickr? Those aren't good examples of cloud services to me because I think the biggest benefit of the cloud is that you can stop using a service but still have access to your data.
I'm curious as to why you think Dropbox isn't a good example. You can walk away at any time and all your data is still exactly where it was last sync'd. That seems to be ideal.
The Dropbox app creates a local copy of your data that will sync with your data in the cloud. The result of this is that you always have a local copy of your data. If you stop using Dropbox all the data remains where it is on your computer.
Ok, you do have (kinda) a point with Dropbox since they store the file locally on all computers.
What I'm saying though, is that the cloud storage (not local) can be decoupled from the service. Such that if I decide I don't want to use Dropbox anymore, I still have a access copy of my files in the cloud - just not via the Dropbox software.
Imagine if Dropbox sync'ed your local files with your personal Amazon S3 bucket. That's what I'm hinting at.
Dropbox and Flickr? Those aren't good examples of cloud services to me because I think the biggest benefit of the cloud is that you can stop using a service but still have access to your data.
I'm working on that :) - http://openphoto.me