Most experienced change and configuration managers would gasp at the seeming low-tech inefficiency of index cards as means to track and report conformance and status. At the same time, it is hard to combat the efficacy of index cards to engage customers in a more participative and collaborative dialogue for eliciting requirements, and drawing simple diagrams - apparently, the physicality and tactile experience of the cards is simply more inviting and lets the customer do the writing instead of relying upon a single input-controlling scribe. (Some have suggested pair writing could be done between a developer and a customer in the same fashion that pair programming is done during implementation).
Even if index cards are used as the medium for initial capture of requests and requirements, many (if not most) change and configuration managers will want to subsequently transfer this information into a spreadsheet or a tracking system for fast and easy reporting, querying, searching, sorting, as well as for real-time dissemination across the project's organization and stakeholder-sites (not to mention affording more efficient and reliable storage, record retention, archival, and retrieval/recovery). Keeping stories in a tool also lets you apply a simple workflow see how the work is progressing.
Several agilists would argue that such a tool rails against the mandate of simplicity. To be certain, many have gone overboard with defining and enforcing process through a tool - we highly recommend against that since it often results in drastically increased administration overhead, drastically decreased face-to-face communication, and hence very low agility. On the other hand, many have had bad experiences with tools used to enforce too much process. We believe this, combined with bad experiences from misapplied CMM level climbing attempts, is responsible for much of the agile community's backlash against the use of more sophisticated but useful tools and processes.
The relentless focus on keeping things as simple as possible, and on face-to-face interaction over face-to-machine interaction still provides sound guidelines and important reminders when adopting processes and tools. With the right amount of process using a simple and smart tool, agile projects will find increased productivity and better coordination. The bottom line is really to do what you know works for you, and keep it as simple as possible, applying the principles of lean development  every step of the way.
Change management is concerned with controlling and tracking changes to project and product scope and ensuring conformance to customer expectations. Agile change management is concerned with increasing the ability of the project to be responsive to requests for change and to quickly implement accepted change requests. This requires minimizing: the cost of effective knowledge transfer, the amount of knowledge captured in intermediate artifacts, and the time between making a decision and learning the effects of its result. The key success factors of agile change management are the use of iterative and incremental development with short feedback cycles, and close collaboration with frequent face-to-face interaction between developers and customers.
Sometimes the customer base is diverse and/or dispersed and a product manager role is needed to facilitate agreement from, and make decisions on behalf of the customer base. Participatory decision-making tends to produce the most collaborative results, and normative voting and effort allocation approaches have proved effective in reaching customer consensus to prioritize and plan the requests to implement at the beginning of an iteration. The product manager should be empowered to make decisions about issues that arise during an iteration, but either the product manager or a small sampling of customer reps can elaborate the details of a particular request to be implemented.
Index cards can be an effective means of engaging the customer during requirements capture, and simple tools (and processes) are an effective means of tracking, coordinating, and reporting visible progress of requests and changes against expected functionality and content. Don't be fooled by the allure of sophisticated processes and tools; and don't overcompensate by discarding simple but effective tools and techniques. Look for a balance of utility and simplicity that is both effective and efficient in meeting your change management needs. And keep an eye out for opportunities to eliminate redundant or unused elements of your processes, tools, and artifacts after each iteration.