Burndown Charts, Wikis & Spreadsheets

We have been executing a new client project using a set of iterative development tools & techniques, with Scrum as the overarching management process delivering on 30-day deliverable cycles. Accordingly, the burndown chart has been updated daily based on the work effort remaining for each task the team has defined in its iteration backlog. In general, when we show and examine burndown charts with clients for the first time, there is definitely a "wow" factor, as this simple visual display contains almost all of the information they need to readily understand the project status. When we then present this information to clients via a Lab49 client wiki page (we use Confluence ), which contains a continuously updated set of issues & impediments, it tells a very detailed account of the project and gives the clients more transparency than they have seen before. For this particular iteration, we thought we would try using Google spreadsheets to manage the tasks & work remaining -- this has been decent tool to allow a single-point for the entire team to update progress and Google's (AJAX?) front end offers a decent chatroom function for those viewing the spreadsheet. Like a few other collaborative spreadsheet services I have tried (such as Num Sum) the lack of charting is a pain as I have to export the data to Excel but all in all the benefits of the collaborative data management outweighs this. I have tried other agile tools such as XPlanner, but often pefer the simplicity and flexibility of a spreadsheet. Going back to the burndown .... most traditional project management techniques do not provide an intuitiveand simple way for the team (and client) to review how the project is progressing on a daily basis, nor do they provide such a granular level of refactoring of estimates of work remaining.  One of the interesting things in looking at the burndown is the easy nature by which the team can see how far ahead/behind schedule (relative to a "perfect burndown") the iteration is at any point in time. (This key feature is not readily available in traditional techniques). However, the daily inspection of both task-level work effort and iteration progress provides a higher frequency of datapoints, which in turn drives a really granular view of trend shifts where small deltas in the overall trend might actually highlight underlying issues and risks that may have otherwise have gone unnoticed. In other words, the trend is can be more insightful as the data itself. What I would really like to have is a truly collaborative online spreadsheeting function that contains more powerful formatting, analytical and graphing functionality, that I can then reference in-line from my client wiki page to provide truly dynamic updates. I see (one example here) that Dan Bricklin ( the co-inventor of the original spreadsheet - VisiCalc) has developed WikiCalc has some ideas in motion, including working closely with Socialtext. Other suggestions welcome ...