To give myself some small sense of how confused users will be when confronted with mashed-up identity systems, I've created an account at OpenID France.
Canadianness notwithstanding, "Je ne parle pas le Francais".
Even though there was only a single system in play, I expect that the frustration I felt from initially trying to present my OpenID there (unsuccessfully, I eventually realized it's a FOP (French OP) and not a FRP) is representative of future user confusion when confronted with new & unfamiliar identity UI (granted that most users will not chant poorly-pronounced French-Canadian curses referencing Catholic icons under their breath in order to deal with said frustration).
Ah, OK, so this card thingy carries my OpenID thingy (which sometimes I just type in?) and its a managed thingy I think whatever that is, and because the card thingy has a pin thingy assigned I have to sign-in to the OpenID thingy both here and when I get sent over to the OpenID place when normally I just do that once but thats OK because I've used my cat's name for both, and by the way WTF is a SAML?