More info at http://www.riolinx.com/en/blog/Lists/Posts/Post.aspx?ID=36

Standard Edition

Standard Edition Includes:

Fully Packaged Installer User and Group Management

Delegated Administration User Segregation/Multi-tenancy

People Picker Visibility Restriction ForeFront UAG Integration

Customizable Email Notifications Multilingual User Interface Mixed Authentication Support

Auto Sign In for Windows users Sign Up Web Part

Password Update/Reset Profile Update

Password Strength Policy Account Lockout Policy

Standard Edition Features Plus:

Account Expiration Policy Account Expiration Email Warnings

Account Expiration Reports User Invitations

Dynamic Registration Rules Registration Approval Workflow

Auditing People Picker Enhancements

Professional Edition Features Plus:

LDAP Directory Integration

Professional Edition

Professional Plus Edition