Issue: Shortly after the "deploying solution packs" step of the installer for the FIM Service and Portal, the installation rolls back without warning or error.  Verbose logging of the install showed the following information preceding a 'return value 3.'

MSI (s) (1C!3C) [13:05:32:956]: Closing MSIHANDLE (179) of type 790531 for thread 4668
MSI (s) (1C!3C) [13:05:33:034]: Creating MSIHANDLE (180) of type 790531 for thread 4668
CAQuietExec:  An exception occurred while running Microsoft.IdentityManagement.SolutionPackUtility.exe: The Web site address "/IdentityManagement" is already in use

Cause: The user performing the install does not have sufficient SharePoint privileges to modify the FIM Portal web site address.  Specifically, the install account was a member of SharePoint Farm Administrators, but not Site collection Administrators.

Solution: Adding the install account to the Site Collection Administrators group in SharePoint and performing an IISRESET allowed the installer to complete successfully.