I'd also like to know what technology is being used behind the scenes
for iGoogle. I've tried to search around for an open source framework
that provides the same basic windowed functionality and customization
that iGoogle provides. Here is what I've found so far:

-Pentaho Dashboards & Dashboard Builder: Appears to be a very mature
open-source framework dashboard with reports and out-of-the-box
features to leverage.
-Spago Solutions: Seems similar to Pentaho, but less mature.
-Apache Jetspeed-2: open-source implementation of JSR-168 (Portlet
Framework), seems to be an implementation to handle common portlet
functionality like security, but I don't think there is much boiler
plate code for making quick widgets/mini-windows
-Websphere Dashboard Framework: Appears to be a non-open-source
framework for building a dashboard with reporting capabilities. I
would guess that you probably have to be using IBM Websphere and their
Portlet solution to use this framework.

If anyone has experience with these frameworks please let me know how
you've found them to work. I've only done a very high level
investigation on each.