Matt Curry has this recent post looking at the CakePHP Status plugin he's developed and how to add in a custom Ajax-powered panel.
Last time we made a simple panel that showed the last 10 users that signed up for you web app. [...] This time we'll do a panel that shows the number of sign ups based on a time frame. We'll add a drop down that let's you select day, week, month or year and it'll show a breakdown of new users for that period. The updates will use ajax.