In SharePoint 2007 we had four site collection administrators for one collection. Now that we're upgrading it looks like you can only have one primary site collection administrator and one secondary site collection administrator in SharePoint 2010. Is this always the case or is there something that I'm missing?
What you're looking at are the primary and secondary site collection administrators that you set upon initial site creation. In addition to being added to the site collection administrator list cited by John Chapman, their logins are also added to the site fields "Owner" and "SecondaryContact". This can be useful in situations where you need to be able to get in touch with one or two top level admins in a given site collection. Admittedly, it can be less than useful if it's a long-standing site and the original owner has left the company.
You should be able to change the Owner and SecondaryContact fields through Powershell.
$site = Get-SPSite http://webapp.com/site $site.Owner = "domain\login" $site.SecondaryContact = "domain\login"