W3C has created a widget spec 1.0 which is an attempt to get all of the widget makers to play nice. Google, Yahoo, Microsoft, and Apple were targeted with this spec since each has their own version of widgets.
This should be an interesting technology in the same vein as AJAX. The spec doesn't quite instill confidence yet, since it is still in draft form. After a bit of research it seems that current widgets run on an existing app (Yahoo's widget engine / Google's desktop app). It will be interesting to see if any of the browsers pick this up. That would be cool.