In System Settings after an upgrade from 12.10 to 13.04 I am not longer able to add Online Accounts. (I noticed this after launching Empathy, which prompted me: "You need to set up an account to see contacts here.") I had an AIM account already configured but was not able to see my AIM contacts. I tried to remove the AIM account and re-add, but the System Settings panes for Online Accounts does not have any fields for adding account info, just: "Please enter your account details Cancel/Done".
Online accounts — and particularly online contacts — don't work properly under 13.04.