Andy Burns has written a nice review of the Lightning Conductor Web Part and does a comparison of other roll-up web parts and techniques available to you in SharePoint.
You can see his review of the LCWP here:
http://www.novolocus.com/2008/07/22/content-roll-up-options-part-iv-lightning-tools-conductor/
And the overall conclusion and review of each option here:
http://www.novolocus.com/2008/07/24/content-roll-up-options-conclusions/
