Last month I was working on a demo for a charitable organization that has lots of volunteers around the country. The charity didn’t want to have to create new active directory accounts for each of these volunteers so as part of the demo we integrated SharePoint 2010 site with Windows Azure App Fabric Access Control (ACS), this way we could use Google, Windows Live, and Yahoo! as authentication providers. (Yes I know we could hook directly to each of these providers, but using ACS allowed me to use all the providers with one SharePoint Trusted Provider instead of using three different trust providers). We demoed the site to the charity and they were very excited and happy with the solution.