Just to throw in some comments here...
We used to have Sysprep images for some time until we went to WinXP, where we decided to move away from Sysprep towards unattended installs of the OS. This brings plenty of advantages and has not yet shown any downside for us (which is an Enterprise environment).
Migrating from x32 to x64 is also simple and overall we stay hardware indipendent. This is also a clean solution and does not require such maintenance as sysprep does.
-BBC
PS: We have been running HII since over 7 years successfully against various hardware platforms from different vendors. If anyone should be interested in exact details about the process, I'm happy to post them.