[zope] extra data for users

[Ian!]

Sorry if this is a newbie question, but I'm having a hard time finding
general advice on this. I'm really new to zope.

I'm running zope, CFM and plone. I am trying to build a "secret santa"
system, where each user will eventually be given the address and name of
another user that they will send a gift to. This means that each user needs
to have the additional "address" and "gives-to" fields.

Can someone give a recommendation of how I should store this extra data?
Should I extend the zope users, or should I store the data with the CFM
member's folder (what format would this be?), or should I put it all in a
database?

Ideally I'd have the data with the zope user object, so that when someone
deletes themself from the system I can track down their recipient and find
the recipient a new giver. Is there an easy way to add new attributes to the
user, and are they easily modified after the user is created?