Faster Installs using MSIFASTINSTALL


When set, this property makes a large Windows Installer package perform a faster installation. The property can be set on the command line or in the Property table to configure operations that the user or developer determines are non-essential for the installation. The value of the MSIFASTINSTALL property can be a combination of the following values. It is available only in Windows Installer 5.0 and later.

Alex Verboon has tested this property (MSIFASTINSTALL) with a couple of installers and shared his results on how this property helped in reducing the installation time on Windows 7.
Check this link for more information.