Haven't seen it in action... but this sounds pretty freaking cool....
What's New Web Part for SharePoint Sites
Source code for a Web Part that walks through an entire site using the WSS object model and returns the most recently changed entries.
http://www.gotdotnet.com/Community/UserSamples/Details.aspx?SampleGuid=d46d371b-6300-4f17-b888-bef44baed017