I'm a big fan of unattended builds and I've been using them for over five years now. The process of creating an unattended build can be somewhat hit and miss so using something like VMWare to test the final build is often an essential.
nLite has been around for a while but the last time I used it I found that the resultant build could be flaky and often just not work.
These issues seems to have been fixed with current version as it's remarkably easy to create a custom build and to add service packs, drivers and patches.
Overall I'm very impressed with the tool and at price tag which is free I really cannot complain!