The other day was about Tomboy notes, today, Evolution contacts syncing to Ubuntu One!
For the basic setup, see this tutorial. So, once you have contacts in the Evolution CouchDB Ubuntu One addressbook, syncing to Ubuntu One happens automatically:
The same contacts show up automatically in the Ubuntu One web UI:
Now, we just need to get mobile devices (N900, Android, etc) to sync contacts there also, and your contacts would be everywhere you need them!