Meanwhile I work for a major US IB. While I don't work on anything customer facing our internal SSO infrastructure basically consists of a single cookie that gets access to almost everything.. And its really not difficult to sniff one from another user (like say getting them to visit a link like
http://mydesktop.companyname.com/..).
Its so bad that for certain systems we check the origin of your connection and will only trust you if you've come from the DMZ rather than internal.