I need to Hide "Sections" of InfoPath form using SharePoint or AD group membership (either is fine). How can I achieve this?
InfoPath 2010 in SharePoint 2010
This is a bit tricky as there is no "built-in" way to accomplish this. There are a couple of ways you could go about:
1) Create a separate list that has items with the permissions assigned to them. Then query that list to determine which items that user can see and act accordingly. There is a good blog post about how to do that here: http://stevessharepointnuggets.blogspot.com/2012/05/infopath-2010-restricting-control.html
2) Use the SharePoint web services to query the information you want from the user profile service. This is a bit more complicated than #1. There is a good blog post about how to do this here: http://info.akgroup.com/blog-0/bid/69277/InfoPath-Restrict-visibility-to-users-in-a-SharePoint-Group
In an InfoPath form, you can create multiple views. Create as many views as you need then apply the rules to the views based on the current user permission.
To achieve the permission check you need to get the group membership from the UserProfile service. Here's a detailed article that mentions about how to set up such permission check within Infopath 2010.