Note: any temporary boost in readership as a result of possible confusion with a frequently searched project dealing with identity and the card metaphor is purely coincidental.
I searched for 'identity card art' (motivated by this and this) and discovered the Identity Card Concept Project an interesting exploration of possible future variations on today's business card - organized into themes of true identity , digital identity, control, memory, ritual, and branding.
Two of the control proposals, the Perforated and Onion Card feel very user-centric, the owner of a business card would be able to customize his/her card in real time to the context (who, what, where, why, when) in which it was being presented.
For the perforated card, each bit of identity could be punched out if inappropriate for a particular recipient. The idea could be taken one step further with some sort of punch table (like for 3-ring binders) that would, upon appropriate configuration (e.g. turn the 'When' lever to 'Friday Night' and the 'Why' lever to 'Dating'), remove all irrelevant identity. People would want to tailor their 'IdentiStampers' (Copyright Pending) to suit their tastes I'm sure.
I found the description of the Onion Card particularly interesting - it paints a picture of negotiation and progressive disclosure - each participant sharing more information as their partner does. A "You show me yours and I'll show you mine" model. It also implies a connection between the physical world in which the card is presented and the digital world in which the identity is stored (and a market for compact bar code readers). I do think the cards would look much cooler if they used QR-codes.
While in the Perforated model the user holds their identity themself (under the mattress as it were); in the Onion Card model they carry only pointers to the identity, the actual data is held elsewhere on their behalf by some trusted 3rd-party and released upon successful request (with the bar codes acting as bearer tokens).