I have used the unified configuration in the past and it works fine. The only advantage as you stated is having the drivers loaded for you,raid controller, nic, etc etc.. Of course in 2008 this isn't an issue as you get options to load needed drivers such as the broadcom chipsets or raid controller drivers during setup..
Another benefit of the unified configuration (least it used to be this way) was that it let you save the configuration files on the c drive so you can use them to roll out many other servers using the same unmanaged installation choices you selected for the first one.