We already talked about Darren's tool to investigate Group Policy performance, so here's what some other GP MVPs are up to:
Jeremy Moskowitz blogs about how to use his product, PolicyPak, to disable various 3rd party software through Group Policy.
Derek Melber has launched a new site, http://auditingwindowsexpert.com/.
Alan Burchill has written best practice guides for Active Directory and Group Policy design .