I do not use an admin-account as my default account. That is usually not a problem since OS X asks for credentials for an administrator when needed. On OmniWeb sneaky peaks with the latest update and restart functionality it seems the process of updating the app hangs and doesn't get trough to the point where this is needed. The update on my machine works when logged in as admin but not as a non-admin. That is why I suspect this is the cause.