Ubuntu One is storing your credential inside Gnome Keyring Manager. You can access this manager from the System -> Preferences menu (or in older Ubuntu release from the Applications -> Accessories) choose the application named Passwords and Encryption Keys.
You can see that your Ubuntu One credentials are stored there.
Note that this keyring manager is encrypted, it's a safe store. But it is unlock upon login, so that's why you don't need to enter your Ubuntu One credentials.
Ubuntu One is storing your credential inside Gnome Keyring Manager. You can access this manager from the
System->Preferencesmenu (or in older Ubuntu release from the Applications -> Accessories) choose the application namedPasswords and Encryption Keys.You can see that your Ubuntu One credentials are stored there.
Note that this keyring manager is encrypted, it's a safe store. But it is unlock upon login, so that's why you don't need to enter your Ubuntu One credentials.
It's really worth installing this little indicator-applet to see what Ubuntu One is doing. It's no dropbox, not by a long shot, but I find it helps demystify what on earth U1 is up to at any given moment : http://www.omgubuntu.co.uk/2010/10/ubuntu-one-indicator-applet-puts-sync-status-back-into-view/
Sadly, this proposed upgrade to the Ubuntu One client didn't appear the make the cut for 10.10 : http://www.omgubuntu.co.uk/2010/07/the-ubuntu-one-control-panel-beauty-in-simplicity/